Here's an example of momentum in Hockey. I've seen a team struggling, then player makes a big hit, or puts his health at risk to block a shot, and all of sudden it's like the rest of the team wakes up and gets a dose of adrenaline.
Not counting injuries or penalties, rarely will those things be built into the live wagering. So if you aren't making a lot of money off betting that, it's actually a strong indication it really isn't happening like you say it is.
Aren't there also times when a player risks injury and his team doesn't win? How many times does that happen during the year compared to the number of times a struggling team does "get a dose of adrenaline?"