Ofcourse a person could have a session of batting practice in a lucid dream but my question is…would it really affect your skill IRL???
Hmmm…imagine if it did??..I would so rub it in my friends face…LOL…he doesn’t believe in lucid dreams…and looks at me like I’m crazy everytime I mention it.
FREE BATTING PRACTICE!!!
Yes, LDs can be used for rehersal and furthermore, you are even better at performance(you can sprint faster, kick faster, jump higher,…).
A good example is singing-some reported that they used LDs before their performances on stage, also that they LDed studying before tests.
But weirdly enough it can be done in a ND too. Last week I NDed snowboarding(it was easier, since I was stronger and in better shape).
There was a Quest about it: Improve your skills. There was an international LD experiment and someone also wanted to start an experiment in the lab here. There was also someone who asked whether it is possible to gain muscle etc
It does help if you practice something in a dream, in both normal and lucid dreams as DelThako pointed out. 
You should still keep up the RL practise since dreams and real world work differently. I noticed in one LD that catching a ball was as easy as thinking it. I manipulated the outcome without even trying, I just wanted to catch the ball and I did. The ball came to my hands. Ofcourse this wouldn’t happen IRL, and I suspect it’s hard to try to catch the ball in a dream without manipulating it at all. So, practise, but don’t rely on that practise alone.
As long as you could keep the mind set you have in your dream I dont see why not. The help it gives you would be mostly mental, you would still have to combine it with the physical aspect of fighting