AFCON 2015 Quarter-finals: Deserving Winners or Unlucky Losers?

This weekend was a mammoth weekend of football which obviously means mountains of potential writing material. However, since my recent focus has been on the Africa Cup of Nations tournament, it seems only fair (and logical) to continue in that vein. (And, the less said about Saturday's new-firm semi-final at Hampden the better...)

In my last post I discussed my observation a seemingly large number of goals have been scored in the last 30 minutes of these games. It makes sense, of course, as a knock-out cup tournament like the Africa Cup of Nations is all about the elimination of teams until a winner is crowned. Naturally, teams will push more in the dying minutes as their survival in the competition depends on it.

Luck or Skill?

Another theme of this tournament I have tried to explore is what role luck plays compared to skill. Work done by the excellent James Grayson using English Premiership team-level data has shown that even in leagues, and over time, metrics such as percentage of shots on target or percentage of shots saved boil down to luck much more than skill.

Using data from the bbc football match summaries, I graphed team skill and luck from the quarter-finals. I calculated a team's Shots on Target Ratio as a measure of skill and PDO as a measure of luck. The chart** is below:

Reminder: PDO (Luck) centres on 1000 and is mean-reverting. What this means for the purposes of this explanation is that teams at the higher-end of PDO have had more luck on their side than the teams on the lower-end of PDO. Additionally, we would expect PDO to converge on 1000 over time.

According to the PDO figures in the chart above, the Ivory Coast and Equatorial Guinea were luckier than Ghana and the Democratic Republic of Congo (DRC) were to be victorious in their respective quarter-finals. Ghana, for example, did not allow Guinea a single shot on target in their game and made it look easy. The DRC made a truly inspired comeback against Congo scoring four goals in slightly over 25-minutes. But they also shot nearly double as much as Congo did (21 to Congo's 12).

Hard luck or good tactics? Or, something else?

So, I sat there thinking about luck and skill...

After watching the Ivory Coast manage to beat Algeria 3-1, I thought it would be incredibly difficult to use any figures (apart from goals scored, obviously) to prove that Ivory Coast were deserved winners. Algeria seemed to dominate the pace of play, and seemed to be a much stronger team. Additionally, Ivory Coast looked very shaky in defense.

However, Herve Renard - the Ivory Coast boss - made an insightful comment about how he arranged his players tactically to overcome the individual strengths of Algeria, a team he considered the 'best in the tournament'. He told the BBC:

"We needed to be very well-organised and try to counter a team who are very strong individually." (emphasis my own)

In the same interview, Renard explained he thought Algeria were much better on the ball and going forward, but he set his team up specifically to make the most of the pace of the likes of Gervinho and Max Gradel to supply Wilfried Bony on counter-attacks. And, it worked.

Algeria themselves played a different kind of game to how they played in the group stages: they had more possession and shot more. In the group stages they averaged under 50% of the possession in games. In this quarter-final they had 60% of the possession. In the group stages they took around 7 shots per game (on avg.). In this game, they took double that, 14 shots. But Ivory Coast had all the right answers to Algeria's change of style. And, Ivory Coast had Wilfried Bony to thank who scored twice and drew Algerian defenders to foul him four times. Algeria could have done with a presence like his in their attack...

In the Tunisia-Equatorial Guinea match, however, I think poor refereeing luck played a huge role in assisting the hosts progress to the Semi-final. An extremely soft penalty awarded to Equatorial Guinea in second-half stoppage time seemed to be so unfair on Tunisia. I think the image below says much more than my words can...

I think this @AP image pretty much sums up the Tunisian mood right now... #AFCON2015 pic.twitter.com/urAwWRxF7k
— Joe Crann (@YesWeCrann) January 31, 2015

Dominance in the Quarter-Finals? Or, was it really luck?

I also wanted to look at the games in another way so I looked at the shot-dominance in the quarter-finals. Recall from my earlier post when I dived into a preliminary statistical sweep of the group games that the sweet-spot of the graph below is the bottom-right corner. This is where teams take many shots and limit the number of shots taken against them. In this corner is Algeria and the DRC. Now, from the PDO vs. SoTR chart above we already established the DRC ran out deserved winners. And, from what Renard said about his tactics against Algeria we see that the counter-attacking style of play is not well accounted for in these charts. 

chart concept from Ben Mayhew of experimental361.com

An interesting part in the chart below is how closely matched Equatorial Guinea and Tunisia were over the course of 120 minutes - at least in terms of shots. Again, it is hard for these charts to take refereeing decisions into account...

** Updated on 2/2/15 at 16:30 to include revised PDO chart