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Feb 19, 2015
Feb 19, 2015

Overweighing the importance of first half goals in soccer

Overweighing the importance of first half goals in soccer
When betting on soccer live bettors must be wary of falling into a trap of being swayed by events that occur in a relatively short space of time. This article looks at why bettors shouldn't overweigh the importance of a goal glut in the first half.

A rapid sequence of events, most notably multiple goals in a short timeframe are always memorable, but they are almost always uncharacteristic of the way in which a soccer match is played out.

This can lead to either an overreaction by live bettors as to how the course of a match will continue or how sides will perform subsequently in other contests by pregame bettors.

Chelsea vs. Bradford – An example of short termism & small sample size

Bradford City’s four-goal reply to falling 2-0 behind at Chelsea was astonishing. But it would be unwise to rely on this evidence to project Chelsea as being inferior to a mid-table League one side.

Small sample sizes can throw up anomalies, and if Chelsea were to play Bradford City numerous times would almost certainly prove themselves the superior team.

Chelsea are unlikely to have the opportunity to gain revenge in the near future for Bradford City’s audacious feat of scoring at the rate of a goal every 13 minutes for just over a half of soccer.

A typical Premier League game will have an average of 1.19 first half goals and 1.45 second half scores

But we can use the scoring feats of a wider batch of sides to illustrate that rare and unusual scoring patterns that will inevitably appear in matches are poor indicators of what might occur generally in the future.

Goalscoring pattern analysis in soccer

The average number of goals scored in the Premier League per game over the past decade is just over 2.6 goals. This number tends to rise as the gap between the relative strengths of the teams increases.

So two evenly matched teams might be expected to average less than the league average total goals and a mismatch between top and bottom might expect to see the average creep towards 3 goals per game.

The plot below shows how the probability of a particular number of goals being scored in a Premier League match changes as the favourite has an increased per-game likelihood of winning the contest. Goalless games become less likely as the gap in quality between the sides increases, while the chances of a game having 4 goals becomes more likely as the size of the mismatch increases.

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55% of the total goals are scored in the second half, as players begin to tire and more risks are taken. So in addition to the relative pre-game supremacy of the favourite driving total goals, we should expect, on average to see more goals scored in the second half than in the first.  

A typical Premier League game will have an average of 1.19 first half goals and 1.45 second half scores. However, these figures are just averages. Nearly 70% of Premier League games had one or fewer first half goals, but over 10% of matches witnessed three or more goals being scored prior to the interval.

There are two scenarios that could be played out in matches where three or more goals are scored in the opening 45 minutes. If short-term recently occurring events are more important in determining the course of a game, we might expect to see the frequency of the scoring to continue into the second period when the first half has been full of goals.

Longer term trends are always more predictive of future events than short bursts of atypical performance

However, if, as we surmised with the Chelsea and Bradford City example, apparently unusual scoring rates are bound to happen from time to time, merely through random variation, we should expect subsequent events in the second half to more closely resemble our pre-game expectations based on the relative strengths of the two teams.

Over a five season period, Premier League matches where three or more goals were scored in the opening half, had an average of 1.6 goals in the second period. This compares to 1.52 goals per second half that were scored in games where one or fewer goals were recorded before the break.

So superficially it does appear that lots of goals in the opening 45 minutes do lead to more scoring in the second half, although the rise is small.

However, as we have seen in the plot above, the total goal expectation for a match is also dependent upon the gap in quality between the competing teams. And matches where three or more goals were scored in the first half in the sample also featured more short priced favourites than those games where scoring was scarcer in the first 45 minutes.

And once we account for this competitive imbalance between the two groups of matches, the number of goals scored in the second period of matches with 3 or more first half goals tallies closely with our pre-game estimates of how many second half goals would be scored.

Conclusion

In short, events, such as goals can occur in clumps quite naturally. But this shouldn’t be taken as a sign that rapid rates of scoring will continue within the game or that a team has suddenly become much improved or suddenly poorer than they have previously shown.

Longer term trends are always more predictive of future events than short bursts of atypical performance.

First half goal gluts don’t on average herald a continuation of higher than normal scoring, even within the same match and Chelsea can also continue to be confident that they will remain among the dominant Premier League teams, despite the short term heroics of their FA Cup conquerors, Bradford City.

This article therefore explains to bettors the danger in drawing faulty conclusions from limited, but memorable events, such as one off results or a large number of goals in the first half.

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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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