This review says telephoto autofocus speeds haven't been the best with Nikon's other extreme megazoom cameras, but the company says the P900's lag when fully zoomed in should be 0.75 seconds in overcast conditions. So as long as you're not too tight on your subject and they aren't moving fast (or you're very good at predicting movement) you should be able to get a clean shot.
Probably wouldn't be a bad camera for someone who wanted something cheap and still be able to do some zoom without carrying additional lenses.