Hmm, hardest "singular task" in sports (so "hitting a 147" doesn't count as that's 36 tasks). I'm going for:
- batsman facing a 90mph bowler
- taking an uppercut to chin in boxing/UFC
- MotoGP rider taking a bend at 150mph+
All of them can involve death if you go wrong
Hitting a baseball from a professional pitcher is the hardest singular task in all of sports, and that's not debatable nor is there a close comparison. Say what you want about baseball players' athleticism, but baseball is the purest, most challenging sport in existence.