Pick him up immediately. Bend down, look in his eyes and tell your son (calmly) it's not ok to hit. Hitting hurts and I can't allow you to do it.
Do not give him any attention for a few minutes.
Time-out may work--not for all twos---if u do try it, you must be consistent !!
When he is playing with Grandma or eating with Grandma in a nice manner, compliment that behavior.
Even though kids look passive when watching tv/movies, they are actually tense. Limit the media time.
Kids do kick, hit and bite during the toddler stage. It's how we handle and being consistent that counts.
When my daughter was in the hitting stage, I used to tap a balloon with her (Under my supervision). I would tell her that I was going to hit the balloon up in the air. And we would tap/hit the balloon. I would remind her at that time that hiting people was not allowed. Or we would kick a ball outside...