Knock out stages in European football

21/02/2017 | By | Reply More

Knockout Stages of Champions League

February brings the knockout stages of the Champions league. The group stages tend to eliminate weaker teams from the tournament. The remaining, generally higher quality teams, know they are a few matches away from a shot at the glory of the champions league title. It’s all or nothing from here!

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Incentive to Score & The Away Goal Rule

A huge factor in the knockout stages of a competition is the incentive to score. If a team can qualify to the next stage, there is a huge incentive to do anything to get that critical goal. The absence of that goal will see elimination, so you may as well go for it! The away goal rule enhances this incentive for a goal.

Knockout matches in the Champions league, as with other similar competitions, require that teams get through the next round by winning over two matches, home and away. If the aggregate scores are the same, then away goals count as being worth extra on that aggregate score line over the two legs.

As an example, if a team wins 2-1 at home and loses 1-0 away the aggregate score will be 2-2. The team that scored the one away goal will qualify. The only way the home team can go through is if they win their home leg 2-0 for an aggregate score of 3-2 over the two matches.

Confused by the away goal rule? You are in good company. There has been at least one case of a wrong application of the away goals rule by a referee in an international club tournament. It happened in a second-round tie in the 1971–72 European Cup Winners’ Cup between Rangers and Sporting Clube de Portugal. This fixture ended up 6-6 on aggregate but the referee ended the match with a penalty shootout. Rangers appealed, won the appeal, and went on to win the Cup Winners’ Cup that season.

Setting up a good second leg

The away goal rule was created to create an incentive for goals, but you sense this often backfires. If an away team can hold out for a low score or perhaps sneak an away goal, then the return leg is a promising prospect at home, where home advantage can play a hand towards qualification.

We analysed all the round of 16 matches since 2008 and found that this concept of holding out for a low score in the first leg appears to be true. Since 2008 the first leg has produced just 2.48 goals versus 3.25 for the second leg.

If we broaden our view of the market to look at the actual deficit a team takes in to the second-leg, we get a clearer picture of how things are likely to play out given a certain 1st leg lead.

A home team carrying a one-goal advantage into the second leg will qualify 56% of the time. If they carry no advantage into the second leg then that drops to 26%. Carrying a one-goal deficit into the second leg means it’s very tough to qualify from that position. It seems you simply can’t afford to lose at home in the first leg.

To see the benefit for the away team you simply invert these numbers in the other direction. For example, an away team carrying a one-goal advantage into the second leg has a 90% chance of qualification. Away goals are important.

If the home team draws 1-1 in the first leg, this puts them at a slight disadvantage in the second leg. The away goal means that on the return leg a slender one goal win will be enough for the home team and that’s clearly a situation that is more likely to occur.

Incentive to score

While trying to understand the impact of different score-lines and deficits, I thought it would be interesting to see if the incentive score rises or falls depending upon the first leg score.

I measured a draw as a ‘zero deficit’ between teams, so it’s important to understand that this doesn’t account for the type of goal. But a ‘zero deficit’ first leg does appear to produce the highest number of goals in the second leg. A one goal advantage will also produce an above average number of goals. In contrast, a one-goal deficit tends to lead to the second leg containing fewer goals. So an evenly balanced match appears to create the biggest incentive for more goals in the second leg.

Stepping back and looking at this, it would appear to be that if a goal is scored in the second leg then you may as well go all out to find the equaliser and the away goal. That would appear to be inflating the number of goals in the second leg.

If a team has dominated the first leg then it’s quite likely that they will sit back and try and defend and not concede any goals in the second leg. If they do manage to score one goal, the tie is effectively over. This is likely to give the home team a slightly more defensive slant until later in the game. You could argue anecdotally that you knew this already, but the numbers confirm it.

It looks like the biggest opportunity comes when the teams are all square after the first leg. Adopting a trading strategy that looks for goals is most sensible in these matches.

When goals are scored

To get some data I compared the group stages with the round of 16. I found that when goals were scored, they seemed to arrive at regular intervals across both parts of the tournament. But when I split the round of 16 into first and second legs, it showed a completely different picture.

In the first leg, as we approach half-time, the rates of scoring look very similar to what you’d expect to see in the group stages. However, if we are in the second leg, there is a slight divergence in the first half that becomes stronger as we approach half-time. By half-time there is about .3 of a goal more in the match than versus the first leg. As we head into the second half the first 15 minutes this widens to .4 and once we pass 60 minutes it widens even further. You can see what is happening here. The longer the match goes on, the harder teams push for a goal. This effect increases when we pass 60 minutes.

You generally see in the first part of the match, that the differential is there. But this gets much stronger when we get into the last 30 minutes of the match. It would appear that as a team faces elimination they’re more likely to make changes to the team and seek that elusive goal that will take them through to the next stages. You can see this clearly within the stats that we collected.

Overall summary

Teams that are unable to defeat their opponents in the first leg at home, will face a much tougher task when they play the return leg away. There is a clear incentive for the away team to try not concede and to perhaps try and sneak an away goal. This manifests itself in terms of the first legs, generally, having fewer goals. If you have two evenly matched teams in the first leg it would seem to make sense to pursue strategies and tactics that exploit the lower goal scoring rate. I can’t stress enough though, that this is dependant on the style’s of the two teams.

The second leg is very much dependent upon what happens in the first, rather obviously. But it tends to lead to more goals and the rate at which they occur tends to be proportional to what is required to qualify. If there are only one or two goals needed, then expect a fun final 30 minute spell as teams pursue qualification to the next round. Strategies that exploit late goals, or more of them, would seem to suit the second leg of a knockout competition.

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Category: Trading strategies

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