BLOG Opta's Event Definitions02 October 2013
Opta's key strength is the ability to provide in-depth, accessible data that is consistent across the globe. Without this certainty, Opta's player and team statistics can be far less valuable and there would be a danger that different leagues would be analysed in conflicting ways, rendering proper player comparison invalid.
To avoid this, Opta have a long-established a consistent list of 'Event Definitions' in football that are adhered to across all data collection centres.
This is a list of the main football events logged by Opta:
While this one may seem obvious, different governing bodies have different rules and Opta usually works with the relevant people to reflect their official decisions on goalscorers.
Shot on target
Any goal attempt that:
a) Goes into the net
b) Would have gone into the net but for being stopped by a goalkeeper's save
c) Would have gone into the net but for being stopped by a defender who is the last man.
Shot off target
Any goal attempt where the ball is going wide of the target, misses the goal or hits the woodwork.
Any goal attempt heading roughly on target toward goal which is blocked by a defender, where there are other defenders or a goalkeeper behind the blocker.
Chance conversion/Goals-to-shots ratio
A calculation of goals scored divided by shots attempted (including blocked attempts).
A calculation of Shots on target divided by all shots (including blocked attempts).
Pattern of play for Goals/Attempts
Set Piece goals/attempts are those where the ball starts from a dead ball situation such as a corner, a free kick, a penalty or a Throw-in and results in a shot before the phase of play has broken down into open play.
The exact point at which it becomes open play is usually clear but set pieces which are cleared and then the ball is put straight back into the penalty area are still deemed to be part of the set piece as the defending team is still positioned to deal with the set play.
A situation where a player should reasonably be expected to score usually in a one-on-one scenario or from very close range.
Expected Goals (xG) measures the quality of a shot based on several variables such as assist type, shot angle and distance from goal, whether it was a headed shot and whether it was defined as a big chance. Adding up a player or team’s expected goals can give us an indication of how many goals a player or team should have scored on average, given the shots they have taken.
The final pass or pass-cum-shot leading to the recipient of the ball scoring a goal.
Fantasy Goal Assist
From Summer 2013, Opta have started to collect a range of other assists used by fantasy football, but also available to clients to determine their own definition should they wish
- Heavily deflected pass
- Shot on target saved, rebound scored
- Shot blocked rebound scored
- Shot hit woodwork rebound scored
- Penalty won
- Free kick won by foul
- Free kick instigated by forced handball
- Instigating own goal through shot/pass
Expected assists (xA) measures the likelihood that a completed pass will become a goal assist. It considers several factors including the type of pass and end-point and length of pass. Adding up a player or team’s expected assists gives us an indication of how many assists a player of team should have had based on their build up and attacking play.
Second Assist/Key Pass
A pass/cross that is instrumental in creating a goal-scoring opportunity, for example a corner or free-kick to a player who then assists an attempt, a chance-creating through ball or cross into a dangerous position.
The final pass or pass-cum-shot leading to the recipient of the ball having an attempt at goal without scoring.
Assists plus Key passes.
An intentional played ball from one player to another.
Opta adds a whole range of qualifiers to each pass event, so that various things can be measured
- Chipped pass - a lofted ball where there is a clear intended recipient
- Headed pass - a header where there is a clear intended recipient
- Launch - a long high ball into space or into an area for players to chase or challenge for the ball
- Cross - a pass from a wide position into a specific area in front of the goal
- Flick-on - a glancing pass with head or foot onto a team mate where the ball is helped on in the same general direction
- Pull back - a pass inside the penalty area which is pulled back from the goal-line to the centre of the penalty area
- Lay-off - a ball returned back to where it came from (usually by a forward) with one touch
- Through Ball - a pass splitting the defence for a team-mate to run on to.
- Each pass is logged with X and Y co-ordinates for its point of origin and destination. This allows Opta to log the following:
- Passes broken down area of the pitch for example by own half/opposition half or defensive/middle/final third or left/right/centre
- Passes broken down by half, for example short/long, short medium/long
- Pass direction, for example backwards/sideways/forwards.
Of course, the event based nature of the data is such that you can calculate any combination such as chipped passes over 20 yards in the final third that go sideways.
Opta also logs whether the pass is from open play or a dead ball situation such as a corner, a free kick, a throw or goalkeeper distribution from hands or goal kicks.
This is simply a formula where Successful passes are divided by Total attempted passes in whichever combination of passes is selected.
Usually, pass completion excludes crosses.
Crosses are usually treated separately and Crossing success is the percentage of successful crosses out of the total attempted.
When the ball bounces off a player and there is no intentional pass, we award a touch. Where there is a mis-control we award an Unsuccessful touch.
This is an attempt by a player to beat an opponent in possession of the ball. A successful dribble means the player beats the defender while retaining possession, unsuccessful ones are where the dribbler is tackled, Opta also log attempted dribbles where the player overruns the ball.
A tackle is defined as where a player connects with the ball in ground challenge where he successfully takes the ball away from the man in possession. All tackles are really a successful event.
A Tackle Won is deemed to be where the tackler or one of his team-mates regains possession as a result of the challenge, or that the ball goes out of play and is "safe".
A Tackle Lost is where a tackle is made but the ball goes to an opposition player.
This is where a player attempts to challenge for the ball and does not make it – it is calculated by adding fouls with an attempted tackle qualifier to challenge lost.
This is a defensive action where a player kicks the ball away from his own goal with no intended recipient of the ball.
This is where a player blocks a shot from an opposing player.
This is where a player intentionally intercepts a pass by moving into the line of the intended ball.
This is where a player wins back the ball when it has gone loose or where the ball has been played directly to him.
Shield ball out of play
Where a player shields the ball from an opponent and is successful in letting it run out of play.
Any infringement that is penalised as foul play by a referee.
Where a player is fouled by an opponent. There is no foul won for a handball or a dive where a free kick is conceded.
Awarded to the player deemed to be in an offside position where a free kick is awarded.
A duel is an 50-50 contest between two players of opposing sides in the match. For every Duel Won there is a corresponding Duel Lost depending on the outcome of the Duel.
Aerial Challenge won - Aerial Challenge lost.
This is where two players challenge in the air against each other. The player that wins the ball is deemed to have won the duel. When more than two players are involved the player closest to the duel winner is given an Aerial Duel lost.
Successful Take-on/Dribble - Challenge lost.
The player who has been beaten is given a Challenge lost if they do not win the ball.
Tackle - Unsuccessful Take-on/Dispossessed .
A tackle is awarded if a player wins the ball from another player who is in possession. If he is attempting to beat the tackler, the other player will get an unsuccessful Take-on. If he is in possession but not attempting to "beat" his man, then he will get a dispossessed.
Smother - Unsuccessful Take-on.
A goalkeeper who comes out and claims the ball at the feet of a forward gets a smother, similar to a tackle.
Foul won-Foul conceded.
The player winning the foul is deemed to have won the duel and the player committing the foul having lost the duel.
A goalkeeper preventing the ball from entering the goal with any part of his body.
Saves are broken down into:
•Caught/Collected/Parried Safe/Parried Danger area/Fingertip
A player or team who does not concede a goal for the full match.
We log which way a goalkeeper dives regardless of the outcome of the penalty.
A high ball that is caught by the goalkeeper
A high ball that is punched clear by the goalkeeper.
A high ball where the goalkeeper gets hands on the ball but drops it from his grasp.
Cross not claimed
When a goalkeeper comes off his goal line to claim a high ball and misses the ball.
The percentage of high balls that a goalkeeper tries to deal with where he is successful - Catches+Punches divided by total high balls he came for.
When a goalkeeper comes out of his goal to sweep up behind his defence and attempt to clear the ball.
A sum of all events where a player touches the ball, so excludes things like Aerial challenge lost or Challenge lost.
For Opta Discipline tables, we award one point per foul conceded, three points per yellow card and six per red card. For Referees' tables we also add three points per penalty awarded.
Sequences are defined as passages of play which belong to one team and are ended by defensive actions, stoppages in play or a shot.
- Sequence Time: Time in seconds of a sequences
- Passes: Number of passes in a sequence
- Progress: Distance in metres the ball moved towards opponent goal line during the sequences
- Length: Total distance in metres the ball travelled during the sequence
- Speed: Length divided by sequence time (average speed of ball movement during sequence)
- Direct Speed: Progress divided by sequence time (average speed of ball movement towards opponent goal line during sequence)
- Width: Distance in metres between leftmost point in sequence and rightmost point in sequence
- Absolute Width: Furthest distance in metres ball is away from centre of the pitch in a sequence
- Involvement: Number of sequences that a player was involved in, involvement is defined as a player having at least one touch in the sequence
Possessions are defined as one or more sequences in a row belonging to the same team. A possession is ended by the opposition gaining control of the ball.
Defensive Coverage measures the area of defensive responsibility implied by a player’s defensive actions during a match. The corresponding output consists of a series of coordinates which define a polygon of the player’s defensive zone, as well as the area (in metres squared) of that zone.
Posted by Rob Bateman at 10:00