I can see an argument has developed on crowd effectiveness so I'm going to wade in here, there is such a thing called Home Field Advantage whereby the crowd can in fact influence the team scoring goals, read more about it here:
You could look at how many goals are scored or conceded at The Valley in the last 5-10 minutes when the stadium is virtually deserted by those "beating the traffic"
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http://www.pinnaclesports.com/online-betting-articles/strategy/soccer/hfa.aspx