I played baseball from the age of 3 until I turned 19. I now play tennis. You cannot compare the fear you feel in baseball to anything in tennis. You cannot call a baseball player a wuss when they constantly have a projectile flying at them at upwards of 90mph that (unlike a tennis ball) can do serious damage. When I was 11 I cracked an opponents rib by hitting them with a pitch. Once again, at the age of 11. Imagine what older/more skilled people do. Thankfully I never had any severe injuries in my time, but I've seen quite a few bad ones.
On the flip side, I would argue they're basically the same level of "manliness". Every sport you play there's going to be a testosterone, jacked up, I'm better than you, type feeling. In baseball I always got it when I struck someone out on a fastball. There was something to the feeling of my best being better than yours. The hitter most likely knew it was coming and still couldn't hit it. It gets you pumped up. In tennis I get the same feeling when I hit an ace, or even more so when I hit a return winner. I don't know why on the return winner other than that the other person is supposed to be in control of the point with the serve and then I immediately take it away. Anyway...
Tennis is no doubt more physically demanding, and that's not a contest. But there's an argument to be made that being a high level baseball player (specifically a hitter) is harder than being a high level tennis player. I personally don't care which is harder. I love both sports and just wish I was much better at them.
Beating someone up is scary for the person being beaten up, and does that make the person being beat up manly?