Originally posted on 10/12/2016:

The chance of scoring on an attack in soccer is an average number of goals by team over number of possessions. An average number of possessions per team is around 100 average number of goals is 1.5,
so the chance of scoring on each possession is 1,5/100 equals 1.5 %, therefore a team that has the ball first is that much closer to win the game than the opponent given other factors are even.