This blog is a longer (and revised) version of my poster at the OptaPro Sports Analytic forum 2015, held in London on 5th February 2015.
When a team is goal down or up, a manager may change tactics (formation) in order to protect the advantage or chase the match. This is more likely to happen at the beginning of the second half, or in the last quarter of a match. Normally, in the first case, there is a change of tactics when a team is losing. In the last quarter of a match substitutes are introduced to either to hold onto winning score, or to chase a losing game. Also, at this time, if his team is winning, a manager may decide to settle for a draw, and change tactics accordingly.
A change of tactics is normally highlighted by match commentators and pundits if the match is broadcast live, or during a post-match video analysis. In contrast to this traditional method of analysis, this poster aims to discover any change of tactics by a team solely by analysing match event data, as provided by Opta.
We are not aware of previous attempt to this kind of analysis by using solely match data. The original intention was in fact to use match data, as characterized by Opta f24 feed, and player tracking data from TRACAB. Unfortunately attempts to use TRACAB data were not successful, and after much trying we decided to postpone such analysis to a later date.
Data and methods
The match analysed is the Newcastle-Hull played in Newcastle in the 2013-14 season. The match data was provided by Opta in the form of f24 match file. The analysis was carried out using statistical and graphical methods. The statistical analysis in particular relies heavily on the technique of classification and regression trees. Both software used are designed for interactive analysis, and therefore particularly suited for exploratory analysis. MS Excel was also used for data preparation and parsing, as well as to create some graphs.
The discovery of tactical changes boils down to finding significant changes in performance by the two teams in the various contexts that characterize a game, for example between he 1st and 2nd half, or before/after a goal taken/scored. This and other contexts, such as before/after substitutions, and in between one time interval and the next are analysed, with ten interval/time segments used for the latter.
The changes that we looked for were:
1. Change in players’ position following a goal (for/against)
2. Change of role/position of substitutes compared with starting players
3. Change in activity (ball touches) by the teams during the course of the match
4. Change in activity in the final 3rd
To identify changes, the following variables were added to the Opta data:
1. Goal_T = G_0-0, G_0_1, etc., to identify time segments when the score was 0-0, 1-0, etc.
2. Final_3rd= 1 Final_3rd ball touches (0=all other ball touches)
3. Xo, Yo = (0,100) coordinates of pitch position of ball touches
Ideally, such analysis should look at the performance of both teams. But because of time (and space) we focus mainly on Newcastle’s performance.
Newcastle-Hull 2-3 (2-1)
Goals: Remy(N) 9’, Brady(H) 25’, Remy(N) 43’, Elmohamady(H) 47’, Aluko(H) 75’
Fig.1 Possession (ball touches) comparison by Team and goal-time intervals
Fig. 1 We compare Newcastle and Hull ball touches, and we find we find that their average X_o position (length of the pitch) is significantly different (SD). Newcastle has significantly more possession the attacking half. This advantage increase after Hull draws 1-1 (G_1-1) but falls as soon as Newcastle goes ahead (G_2-1)
Fig.2 Possession (ball touches) comparison by Role and goal-time intervals
Fig. 2 show the increased activity of Newcastle midfield after the draw by Hull (2-2), and its steep decline by the Fwd after going ahead (2-1).
Fig. 3 Average X position comparison
Fig.3 Here we analyse the average X position of both teams, and we find that Newcastle’s one was closer to the halfway line than Hull (SD), sign of a more attacking stance. Revealing of tactics is the position of Newcastle subs: they line up with the Full Backs (Wing backs, really), a defensive position they kept until Hull went ahead (2-3).
Fig. 4 Ball touches in the Final 3rd
Fig .4 Here we compare ball touches in the Final_3rd. Overall Newcastle was significantly (SD) more active in the final 3rd, but the Subs were below the team average. Goals for/against did not result in any significant change of activity in the final 3rd. However the Subs were active mainly in the centre, in contrast to the centre-right of the forwards they replaced.
Fig. 6 X position – subs vs. starting players
Fig. 6 Here we compare Newcastle subs average position (X_o) with that of the players they replaced, and find that they took a more defensive position (SD).
Fig. 7 Significant changes in position by some Hull players
Fig.7 The position of ball touches of these two Hull players in the 1st and 2nd half looks significantly different, and strongly suggest a change of tactics in the 2nd half. The stats analysis in Fig. 8 confirms this visual intuition.
Fig. 8 Significant changes in position by some Hull players – stats
Fig. 8 this graph confirms statistically the intuition from Fig. 7. Both Hull goal scorers: Elmohmady (2-2, 47’), and Aluko (2-3, 75’, changed their positions significantly in the 2nd half). Aluko moved from left to right (Y), and Elmohamady forward (X).
Fig 9. Final 3rd ball touches by goal-time interval
Fig. 9 shows the position of ball touches in the Final 3rd by the two teams taken during each score interval. A chart comparing the stats count is shown above
Fig. 10 Final 3rd ball touches by Half
Fig. 10 Final 3rd ball touches – the black horizontal line show the average position of ball touches in each half. Hull’ average changes from left to right (significantly, as shown in the following graph), while Newcastle’s stays roughly the same.
Fig. 11 Final 3rd ball touches – Vertical positional shift by Half
Fig. 11 Final 3rd average Y position – The graph shows that Hull changed its attacking direction from the left to the right in the 2nd half (period_id) – this change was statistically significant( SD). In contrast, after an initial switch, Newcastle kept to a central position for the rest of he match.
The analysis identified some significant changes in performance during the match that suggests a change of tactics. In particular, tactical changes by Newcastle can be said to have taken place after their subs were introduced. Ahead 2-1 with 25min of the match left to play, Newcastle subs took a more defensive position then the player they replaced. In contrast, Hull started the 2nd half by increasing its attacking effort and shifting its direction from left to right; a move that quickly resulted in a goal.
Clues to the above summary conclusion were given by the following results:
Newcastle played significantly (SD) forward than Hull and dominated possession (ball touches) throughout the match, in particular after Hull’s first goal. It was dominant in the final 3rd. Despite of this advantage , Newcastle created fewer chances than Hull, and lost the match
The results suggest that Newcastle did not try hard enough to win the game. Subs introduce at the 65’ when the match was finely poised at 2-2 , took a more defensive stance than their predecessors, and lined up with the full backs (wing backs, really). They only took a more forward position when Hull scored the winning goal, too late to change the result.
Judging by their substitutes performance, Hull appeared to do more to win the game. Their average ball touch position of their subs was equal to that of the Forwards in whole match.
Graphical analysis show s what appears to be a change of tactics by Hull in the second half with Aluko (moving from left to right), and Elmohamady playing more forward. The latter position may help to explain the defensive ball touches of Newcastle subs Guffron and Marveaux in that area of the pitch. It is likely that they were kept busy stopping the threat posed by these Hull players in their left defensive side of the pitch.
(Note: As many would have realised, this analysis is not complete. There are a few other aspects of the match that could have been studied, and could have probably shed more light on the if/when/how changes of tactics in the match occurred. However, the objective of this post was mainly to demonstrate how a data-based analysis with statistical and visual methods could give a more objective view of changes of formation/tactics in a match than one obtained solely by video analysis.)