It is likely a lot of people who post here are athletes, or have been athletes in their youth. So, from most challenging to least challenging sports i have competed in:
Baseball: Hitting a baseball well; took years to become a good hitter.
Tennis: There is a reason tennis fell off in general popularity as a participant sport.
Basketball: Ball handling and shooting; few can do both well.
Football: Sorry; easiest to play. If you can run, you can play. Never played a down of football until I was a freshman in HS; ended up averaging 10 yards a carry. I could run; pure and simple. Nothing hard about it.
Baseball: Hitting a baseball well; took years to become a good hitter.
Tennis: There is a reason tennis fell off in general popularity as a participant sport.
Basketball: Ball handling and shooting; few can do both well.
Football: Sorry; easiest to play. If you can run, you can play. Never played a down of football until I was a freshman in HS; ended up averaging 10 yards a carry. I could run; pure and simple. Nothing hard about it.