5 a side football teams

In a hall there are 14 men playing 5 a side football. Two of the men share the same name.

The teams play games with 10 men. That is, two teams of five men are on the pitch for each game. After a goal is scored, the team which lost the goal leaves the pitch, and the team with only four members comes on, but takes a man from the team leaving the pitch to make up numbers.

The only snag is that it gets confusing for a team to have two players who share the same name, so the teams decide not to allow this, and always choose an alternative team member from the losing team to make up the five.

PUZZLE (in two parts):

Is this disadvantaging the team members with the same name, or is there some formula which favours the team members with the same name which will allow them to redress the balance?

NB the winning team always has the same five players on the pitch that won the previous game in the next game, and will not swap any players.

Some questions:

Is it an advantage, or a disadvantage, to play football? Given the choice of playing football or sitting out in the bar, I know which I would prefer.

Should we assume that the two teams always have an equal chance of winning? If the same-name players are significantly weaker players than the others, they will sit out more than the others regardless of their names.

Given that the players teams will change, this is not a given...

For the sake of argument, then, all the players are of the same skill level...