Dec 29, 2014
Dec 29, 2014

Factors affecting the number of goals scored in a game

How to bet in the over/under goal market in soccer

What is the competitive balance

Factors affecting the number of goals scored in a game
Understanding what factors affect the number of goals scored in a game is vital for betting on the over/under goal market. This article explains what to consider before betting on the number of goals in a game.

The third round of the FA Cup follows quickly on the heels of the packed Christmas and New Year fixtures. And while there may be a handful of shocks, these results are unlikely to be out of step with the individual match odds available.

Collateral form between divisions is fairly well understood, especially as regular promotion and relegation provides a constant re-shuffling of the league pyramid.

A slightly less well-known effect in the FA Cup is the relative goal glut that occurs in the earlier rounds and gradually declines as the final approaches - information that will benefit bettors looking to wager on the over/under goal market of the competition.

The knockout nature of the competition may be used as a possible cause of this elevated level of scoring. As sides hunt an equaliser more aggressively, also exposing themselves to more goals conceded on the counter and then become more cautious in later rounds as the prize gets closer.

Bettors should recognise that outcomes will be determined by a variety of causes

The first round proper of the FA Cup averages nearly three goals per game and this figure steadily drops as the final approaches, falling to around two in the final over the last 20 seasons.

However, a more universal cause is the lop-sided nature of many of the early round matches. Non- league and lower league teams are joined by the top flight elite and even in an unseeded draw, mismatches are commonplace.

Competitive balance

If we also look to the Premier League, the influence of the competitive balance in a match on the average number of goals scored in that game is evident. The more lopsided a contest becomes, the smaller the implied probability will be for one of the contestants to win the match.

For example, a relegation candidate will have around a 5% chance of travelling to a title contender and returning with a win. Such Premier League matches have averaged over 3.5 goals per game over the last 10 EPL seasons and 65% of these games have contained three or more goals.

As in the progressive rounds of the FA Cup, this average number of goals in a game also drops steadily as the competitive balance becomes closer. When both sides have roughly the same chance of winning a contest, the average goals per games has fallen to around 2.5 goals and just 45% of these have three or more goals.

Average goals per EPL game as the pre-game match-ups become more even (2002-2013)

% Chance of an away win% Average goals per gamePercentage of games with 3 or more goals
0-5% 3.65 65
5-10% 3.05 60
10-15% 2.70 48
15-20% 2.67 49
20-25% 2.62 50
25-30% 2.54 49
30-35% 2.48 46
35-40% 2.46 45

Actual data is often noisy because of issues with sample size, but the figures above confirm the usefulness of the Poisson distribution in modelling goals in soccer games. Poisson events that average around three times per game, for example have three or more individual events around 59% of the time. And this fits the actual goal data for matches where the away team has between a 5 and 10% chance of winning from the table above.

Bettors should always recognise that outcomes, such as how many goals a match is likely to have, will be determined by a variety of causes. However, the evidence from both the FA Cup and mismatched games within the EPL does provide good evidence for competitive balance to be a major cause. Bettors pre-match should therefore factor this into their thinking when betting on the over/under goals market.

Individual teams may have consistent team traits, such as being excessively defensive in particular phases of a game. And when two such sides meet they are likely to tweak the baseline figures lower. Also conditions under which a game is played may also have an effect on the likelihood or not of goals being scored.

Competitive balance in a game is the overwhelming factor in determining how many goals are going to be scored

Most notably, initial group matches at major competitions appear to be particularly cautious, regardless of the competitive balance, while final group games or indeed matches in general that are played towards the conclusion of a league season, appear to show a consistent trend towards higher overall scoring.

Local derbies, where the level of support for each team is likely to be heightened have been regarded to be more keenly fought and therefore produce closely contested matches, possibly with fewer goals, regardless of the talent gap between the teams.

Similarly, earlier kick off times may produce the reverse and produce matches that are lacking in urgency and perhaps goals. Players from both teams are playing at a time that is removed from their peak physical performance and supporters are equally lacking in enthusiasm compared to later in the day.

We can attempt to test this by seeing if the added factor of a match being a derby or starting earlier in the day has a significant effect on a goal related market. Neither the kick off time nor the local rivalry of the sides appears to lead to abnormal goal totals being scored in the match once the quality of each team is considered.

It is certainly possible to see patterns of higher or lower scoring in limited numbers of games played under certain circumstances, but these are more likely to have arisen by chance. Instead this article highlights to bettors that the competitive balance in a game is the overwhelming factor in determining how many goals are going to be scored. Factoring this into your thinking before placing a bet on the over/under market is therefore advised.

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Having graduated with a degree in Chemistry, Mark embarked on a career with a major UK brewery. However, his love for sports and numbers was always at the back of his mind. He has been writing about the statistical side of sports, mainly soccer and NFL, for over 20 years and has a particular interest in the randomness and uncertainty inherent in the numbers.
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