~ Luck is another factor. ~
In my opinion, luck is a significant factor in sports betting. Yes, you can analyze the recent performance of the teams, find out about currently injured players, formations and stuff, but all of those things can be done by other bettors too, right? Hence we are getting the odds we can place our bets with. For a team that is very likely to win the odds are usually around 1.10. You have to risk $100 to possibly win just $10. And because of bad luck there can a draw, which is pretty often happens in such cases, and then you lose your $100. So, I'm not sure of to what extent luck affects sports betting, but I feel like it's a big factor.
Speaking strictly formally, luck in betting does not matter at all, since everything is determined by the bookmaker's margin. If you imagine that the bookmaker's margin is negative (in your favor), then you will always win on average (it will seem that you are lucky). For example, if the odds of two outcomes in tennis are 2 and 2.1 and the like, then any better who bets on such odds will be lucky.