As football gradually makes its way into a brave new world of
data and metrics, it is telling that one of the statistics that was
most readily accepted by the community (football, rather than
analytics) remains one of the least well-defined and
Possession statistics are commonplace in football broadcasting
and reporting. They are regularly used to demonstrate one team's
superiority over another, to confirm dominance or otherwise when
the scoreboard remains deadlocked.
However, there is often very little thought given to how this
statistic is calculated. Is it time spent in possession? If so, who
is in possession when the ball is in the air? What if there is a
stoppage in play? Does this get added to the possession log? If it
depends on which team takes control of the ball when it lands, then
when do you stop the clock? This sounds trivial, but it could make
a significant difference to possession statistics for teams that
play in a more direct style. It also requires extra manpower and a
reliance on inconsistent manual methodology, both of which mean
that the 'chess clock' approach would be impossible to apply
effectively across the thousands of matches Opta analyse every
However, if it is calculated solely using completed passes, this
doesn't account for time spent on the ball. It also potentially
overstates the influence of teams who hold on to the ball and play
short passes between defenders or defensive midfielders.
As detailed here Opta uses this second method to
calculate possession, but we accept that neither system is perfect.
The recent Champions League game between Celtic and Barcelona at
Celtic Park highlighted the vagaries in possession recording.
Depending on the source, Celtic's 'possession' was recorded as 11%,
16% or 28%. It is clear that what is a useful way for broadcasters,
other media sources and fans to easily demonstrate the apparent
state of a game, isn't necessarily accurately representing the
Therefore we have looked at a different way of defining and
calculating possession by creating a new framework, with the aim of
improving our understanding and analysis of this notoriously
complicated and misinterpreted subject.
"Half of the people can be part right all of the time,
Some of the people can be all right part of the time.
But all the people can't be all right all of the time"
As Messrs Zimmerman & Lincoln conclude, this may not be to
everybody's taste but we will attempt to set out the rationale
behind the possession(s) framework we have employed:
- (a) possession starts upon a player controlling the ball
This should be pretty straightforward. Specifically, winning a
tackle or header does not, of itself, indicate the start of a
possession. Only the first controlled action thereafter does.
- (a) possession ends when a player no longer has - or tries to
have - control of the ball.
This is where it becomes a bit more open to debate. While it is
straightforward to define a possession ending when a player's pass
is intercepted or they dribble out of play there are some grey
For the purposes of this exercise we are considering launches*
(including long goal kicks) and crosses as 'zonal' passes, into
areas rather than to a specific player. By doing so, the ballplayer
is ceding full control of the ball for the chance of improving
their team's territorial advantage &/or of scoring. Similarly,
any shot is deliberately ending possession with a view to trying to
score - whether the team recovers any potential rebound that ensues
is another matter. Finally, any play-ending event (free kick,
throw-in, corner) is also defined as ending a 'possession' as the
defence can reorganise in the break in play.
At this point, some may be questioning the merits of this
definition. A team could take a goal kick long (1), win the header,
be fouled (2), have a shot hit the post from the ensuing free kick
(3) and score from the rebound (4). At no point has the opponent
touched the ball - never mind possessed it - but this would be
designated as four 'possessions' by the above rules, which may not
sit with a classical definition of possession.
Now, however we can introduce the idea of a 'sequence' - a
series of possessions uninterrupted by an opposition possession.
This allows us to define the above example as one sequence (at this
point it's nomenclature, you can call a sequence a possession and
what we've defined a possession something else if it'd make you
happier), starting with a goal kick and resulting in a goal.
It also allows us more information, now though. A long-ball and
cross-heavy team may take a number of possessions to move the ball
up the pitch, while a short-passing team will likely achieve the
same end in fewer possessions (but more time).
* For a full explanation of launches, please have a look at our
With a defined methodology in place, we can now look at the time
of possession share for both teams. By this method, Celtic
possessed the ball for around 18% of the time. That is, 18% of the
time when either team had possession of the ball. Opta's in-game
measurement using the simplified pass completion method was 16.4%,
whereas measurements from other data suppliers that used the 'chess
clock' approach were around the 30% mark.
Example: Premier League 2012/13
This is obviously only one game and, of itself, doesn't tell us
too much, so we proceed to run the numbers on a group of games. As
teams have had only four matches in the Champions League to date,
we'll try the Premier League on for (sample) size.
For those that don't like staring at a list of numbers, we can
turn this into a pretty(ish) graphic, with the size of the point
representing the teams' time of possession percentage:
As expected, the pass-heavy teams spend the longest on the ball,
both in terms of time per possession and overall time of possession
(which are not quite interchangeable). It is not especially
surprising either to see the likes of Stoke and West Ham giving up
the ball the most readily.
From the other perspective, Liverpool lead the way in limiting
opponents' time per possession, suggesting Brendan Rogers'
high-pass volume/pressing game is getting results, even if it's not
actually gettingresultsjust yet. By contrast, West Brom, Fulham
& Norwich are allowing their opponents a Chelsea-like amount of
time on the ball, possibly indicating a willingness to absorb
pressure and counter-attack, or just that they aren't very good at
imposing themselves on the opposition.
It is worth noting as well, that the spread of the teams' own
time per possession numbers (as opposed to their oppositions) is a
lot larger, suggesting - again, not shockingly - that teams have
considerably more control over their own playing style than their
We can also look at how teams' possession numbers changed based
upon the score at the time. To further boost the sample, we've gone
back to the 2011/12 season and looked at each team's figures when
leading, level and behind. Below is a selection of some of the more
City, and to a lesser extent, United fit the expected - by this
author at least - pattern. That is, taking progressively longer on
the ball when the scoreline is in their favour but at the same time
allowing the opponent more time, with the urgency to make something
happen obviously greater when trailing than when ahead.
Swansea and Wolves display the reverse trend however, while
Fulham's time per possession remained virtually unchanged in all
three states. This suggests that it is simply a function of the
opposition, with the sides spending more time trailing against the
better, more possession-heavy sides. The counter argument to that
is Norwich and Stoke, with both teams' figures remaining consistent
regardless of the score.
A full overview of the 2011/12 season can be seen below.
Obviously the current season is still not even half way through so
any comparison can't be exhaustive. However, the numbers appear to
indicate that Arsenal have been pressing the opposition less
(possibly due to the departures of several players including Alex
Song) and Manchester Utd appear to have been slightly more
pedestrian while on the ball. Again though, be wary of drawing
definitive conclusions from such as small sample.
Clearly, this represents only the first stage in redefining the
measurement of possession in a football match. The graphed results
above seem to tally pretty closely with what we'd expect from
watching the teams play, but there may be better data-led solutions
that we haven't even considered yet.
We'll be releasing more blogs on this subject over the coming
weeks and months. However, please feel free to respond to the
initial work with any comments or criticism. At OptaPro, we believe
the best way to advance any work in this field is by taking a
community approach, and opening our work up for analysis and
critique. Feel free to use the comments section underneath, our LinkedIn group or indeed Twitter (@OptaPro) to
send any feedback.