How Valuable Are Away Goals In Two Legged Ties?

What is an away goal really worth in a two legged cup tie? As we enter the cup season, today on the blog Mark Taylor takes a close look at the true value of away goals.

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Two legged ties have become a staple component of the majority of the knockout footballing competitions played worldwide. England's League Cup competition for Football league and Premiership clubs has maintained two legged ties for the semi final stage throughout its history and has also occasionally included the format for early rounds of the tournament as well as the final itself.

Similarly, World Cup playoff games, promotion and relegation playoffs, the later stages of the UEFA Champions League, Europa League and various domestic continental European club cup competitions all rely heavily on the extended, home and away tie.

Behind these seemingly identical formats there are small, but significant differences in the way that the final goals tally is accounted for. Some competitions also seed the teams and allow the higher seeded side the benefit of playing the second leg at home. This allows them the advantage of playing extra time on home territory if it is allowed for or required and also any penalty shootout is played out in front of a largely sympathetic audience.

However, it is the use of away goals as a tie breaker in the event that the two teams are level at various endpoints that has the most dramatic effect on match outcomes and the dynamics of how ties are played. Some competitions implement the doubling of any away goals after 90 minutes of the second leg instead of resorting to other solutions such as penalty kicks, extra time or replays. While others only take this route after extra time and a few, most notably the MLS and English Football League promotion playoffs have chosen to ignore away goals completely.

The UEFA Champions league apply the away goals rule after 90 minutes of the second leg and then again at the end of extra time. The rule was introduced to encourage a more attacking approach from the visitors in the first leg. Previous formats, where away goals carried no extra weight, on average tended to produce first legs that were tight, low scoring affairs, where the visitors were happy to avoid defeat or take a small defeat and the home team were often unable to break down a packed opposition defence.

Many managers have been credited with recognising the value of seeking an away goal in the opening leg of matches once the change was implemented, among them Johan Cruyff during his time in charge at Barcelona.

Below I've quantified the benefit a team gains from scoring one or more away goals in a first leg compared to suffering an identical margin of defeat where no away goal is scored. As the UEFA Champions league is the highest profile club competition which currently breaks tied matches with away goals and they partly seed their knockout draw, I've simulated a match up that may be typical of the early knockout stages of this competition. All combinations of second leg results and their respective probabilities that lead to the home team progressing are summed to give their likely chance of progressing assuming the relative strengths of both teams remains the same between the first and second legs.

I've pitched the visiting team in the first leg as being overall eight tenths of a goal superior to their hosts, so they would be slightly favoured in the first leg and much larger favourites in the return. An equivalent pairing from this year’s competition would be Manchester City verses Real Madrid or Anderlecht facing Milan. The most interesting scenarios occur when the lower seeded team takes a lead into the second leg.

How Allowing An Opponent To Score An Away Goal Changes A Team's Chances Of Progressing.

1st Leg Home Club Score % Chance of Advancing
1-0 Win. Away Goal Rule 52%
2-1 Win. Away Goal Rule 41%
3-2 Win. Away Goal Rule 36%
4-3 Win. Away Goal Rule 35%
Victory by 1 Goal Margin. No Way Goal Rule 43%

The first table illustrates "Manchester City's" chances of progressing if they achieve various single goal margin wins in the first leg and demonstrates that allowing any away goal is extremely damaging for a team’s prospects. A 1-0 victory makes such two legged ties against "Real Madrid" a near coin toss, partly because it opens up the prospect of the hosts in the first leg grabbing an away goal of their own in the second leg.

Their chances are reduced by 11% if they win by the odd goal in three compared to a simple 1-0, and their chances of progression falls well below 40% in the case of a 3-2 victory. The damage then becomes only marginally worse in the case of higher scoring, odd goal victories.

As an alternative comparison, I've included the likelihood of the home team in this type of tie progressing after any single goal margin win in a format where extra time and penalties are used, but away goals are ignored. The "away goals" format has the virtue of rewarding the home clean sheet compared to an alternative where away scores have no extra value, but the price paid if goals are conceded then becomes a heavy one.

The figures appear to back up Arsene Wenger whose wise words on the subject of scrapping the away goals rule in 2008 included:

"Now, if you play at home and do not concede, it is a good result."

Away goals may have succeeded in encouraging the first leg visitors to play more adventurous football, but it has come at the cost of making the home side very reluctant to risk conceding. The risk and reward has merely been redistributed between the two opponents.

Away Goals And Two Goal Margins Of Victory.

1st Leg Home Club Score % Chance of Advancing
2-0 Win. Away Goal Rule 72%
3-1 Win. Away Goal Rule 64%
4-2 Win. Away Goal Rule 60%

Unsurprisingly, two or three goal first leg leads ensure that even inferior sides are favoured to progress in the tie. But again the concession of a goal on their home turf slices a hefty percentage from their chances compared to a clean sheet. Also a team which appears to be cruising at 3-0 can become much more vulnerable if they allow their opponents to claw the game back to 3-1 and for once the commentator may be right when he suggests that "that goal might just make all the difference".

In this example the chances of winning the tie for the home side fall from a high of 87% at 3-0 all the way down to 64% should the visitors grab a late “consolation” goal to end the match at 3-1.

Away Goals And Three Goal Margins Of Victory.

1st Leg Home Club Score % Chance of Advancing
3-0 Win. Away Goal Rule 87%
4-1 Win. Away Goal Rule 82%
5-2 Win. Away Goal Rule 80%

We are conditioned to evaluate teams by reference to margins of victory or defeat, but in ties where the away goals rule is in operation it is vital that we at least have a passing appreciation of the significance of the actual first leg scoreline and adjust our expectations accordingly.

 

 

Read more of Mark's work on his The Power Of Goals blog

And follow Mark of Twitter: @MarkTaylor0