Gotta ask what are the categories in your league and scoring settings, Tie breaker etc. ? We had this problem in one of my leagues a few years ago when we made innings pitched a category ( was also the tie breaker ugh!) but we put an acquisition's cap of 6 a week and it has made it a lot more interesting. there is still a lot of streaming going on but its more competitive this way, and makes people use there waiver more carefully. But like the guy above said this strategy is of the quantity not quality approach and can often backfire.
One strategy I have used when I know they will just go all out in volume is to pick one or two starts for my aces on my staff so all my quality categories are locked down. I have even just had a rp pitch one inning 3k's no walks no hits, and just benched every one the rest of the week. this was in a 8x8 league though which essentially locked down 4 of the pitching categories. I went really heavy on batting that year so i knew i could get the majority of those, and it worked out. Since then a minimum innings pitched was established. But this is just a strategy u might think about if you feel he is playing dirty, strike back!!!