I have a couple friends who are in the same niche and they live comfortable lives with their IM money. There's two of them, one of them uses affiliate offers and redirects, the other does reviews and gets a commission from each sale. So yeah, Sports niche is viable if you put the effort in. The problem is with how diverse it is, when you say sports, I think football, some one else may think basketball, cricket, hockey, NFL, etc etc endless. So you cannot target a microniche unless you want to. So you need humongously exorbitant (double superlative for a reason) amount of traffic to actually get any converts.