The pros can correct me, but I've read that pro sports photographers may keep 5% or less of the shots they take. Shooting lots and lots is the only way to get a decent number of keepers. Now matter how great a shot you are about to get, an arm, head or ref will get in the way just as you hit the shutter button. Many of the rest will just miss on focus as you try to track the player.
So be prepared to dump alot of pics. It's way better than having very few you want to keep. I use stoppage in play or moments when the play is on the far away from me to try to delete some of the most recent obviously bad shots. I generally plan on one hour of deleting for every hour of shooting after a game.
Having said all that, don't rely on rapid fire bursts alone to get the good shot. Depending on the sport, it is still a good exercise to try to take your shot at the right time. 8 shots/second are almost enough to ensure you'll get your shot, certainly in basketball and football, but some sports such as volleyball or a baseball batter you can still miss the moment when the ball is where you want it. I do find that the rapid fire does seem to help getting shots 2 and on in the best focus so still take an early shot or two. Not sure if that's really true or if I'm just limiting camera movement by the subsequent shots.