Why steriods would help a baseball player
I hate the argument that steroids don't help you hit a baseball. Yes, it takes skill to hit the ball in the first place.
But, look, if anyone seriously believed they didn't help, (a) no one would use them, and, (b) they wouldn't be banned.
If you are stronger, you can swing a heavier bat faster. Bat speed is determined, in fact, by strength. Here is why.
The distance a ball travels when hit is determined by Force. Force is the combination of Mass (weight) of the bat and Acceleration (speed) of the bat. This is Newton's second law of motion.
Think of it this way, you may be able to swing a whiffle ball bat amazingly fast, but it doesn't have enough Mass to propel a baseball far if at all. Conversely, if you bat with a sledgehammer, but can barely get around on it, you won't have success either. Batting is about find the optimum combination of Speed and weight (Mass), to generate the most Force.
The strength of a drug-assisted player gives him (or her) an advantage in that they can use a heavier bat, or swing the same bat faster, generating more Force. Strength is the thing that limits you from swinging a sledgehammer as if it were a whiffle ball bat.