It depends...

I'm not religious at all...but that aside I'll give examples of where it does and doesn't mix.

1. Evander Holyfield...he believes God has got him to where he wants to be and he draws strength from above to win. This to me is an example of someone drawing on something to believe in to make him better so here...it works.

2. Naz...Before, it was never really a problem but if you noticed before the Barrera fight he was saying that "Mohammed is the only God". While I have no problem in someone having their own beliefs, I don't think it's right to force them on somebody else. Plus he received a mass amount of boos, which suggests nobody was interested. I also believe Naz was fairly insecure, and wanted the fans to love him. After his whole Islam entrance, the crowd was pro Barrera and for me, it greatly affected his performance.

(I should point out here that Naz is possibly my favourite fighter of all time)