This is a great time to introduce time outs. I introduced time outs w/my son at 20 mos. After the 2 min were up, I repeated we don't hit/throw/etc. - whatever it was he did that got him into time out. I didn't introduce the word no to my son until he was older. I always said STOP. I didn't want him telling me no, so we (husband and I) just didn't use the word.
When my son hit anyone - as an infant just moving his arms - I started telling him to show them soft. I would take his hand and rub it softly over where he hit. I focused on doing something positive - at an age when time outs wouldn't work. Now at 3, if he hits anyone - accidentally - he rubs where he hit and says I'm sorry - on his own. If he does it on purpose, I give him THE LOOK, and he goes over to the person shows them soft and says I'm sorry. He then goes to a time out.
Your son may not take to time outs right away, but stick with it. Even if he screams and cries. 1-2 mins go by quickly. In time, he'll know that you mean business and that there are consequenses to not doing what you say or not being nice.
Good luck to you.