For my children's sporting events a 300 f4 is a little too long at times. I pretty much have all access since I help coach all of them!, so I'm usually better off mounting an 85 f1.8 and getting down on the sidelines.
Way to many variables! a night scene shot at ISO 6400 might look like garbage. a properly exposed bird in flight shot at ISO 6400 might look superb. and everything in between. The more you shoot the more you learn.