Commentary is dangerous. Commentary is not easy. Don't American Idol yourself (you know, those people who think they can sing then try out and get laughed off the stage...). That's the best advice I could give. If you do decide to go this route with an amateur broadcaster...please please please don't wing it. Go through the cut, write a script, make notes, do multiple takes. Don't do it in a half hour in your basement while the washer and dryer are running.
Couldn't have said it better myself. If you're adding commentary to an edited piece, absolutely have notes on what to say even if you don't script every word. Keep it short and to the point as much as possible, and avoid being overly repetitive.
I think that's the crux of the big complaints about live commentary (i.e. the USDGC comments earlier). They're more or less flying blind on live coverage, seeing it at the same time we see it, and not having any opportunity to think about or prepare what they will say. That kind of situation is ripe for mistakes, repetition and incoherent rambling. There's really no excuse for that on an edited piece.
My advice is go light on commentary (add details that aren't apparent, don't narrate actions that are obvious on screen), leave natural sound in as much as possible, and utilize on-screen graphics to identify players, hole #s, distances, scores, etc. The players on screen are the "stars" of the show, don't overshadow them.