Coming from someone who has friends in the police department, they will listen to your story and never think about it again due to the fact of how random the encounter would be. Without filing a report, they can't really do anything except listen to you and tell you they will keep an eye out for it happening again. If you file a report, they will ask you all types of questions about what the other person looked like, the exact area it happened, and the direction they were heading as well as limitless other questions to narrow down the suspect. After that, they will usually dispatch a few officers to look for the individual matching your description which may or may not have a very negative impact on someone who looks similar to the person who hit you. On top of it all, people generally don't pay attention to specific features of people passing by, so the chances of getting a good look at the person who did this is slim at best.
Bottom line, the best course of action is to hit them back. People who do this as a prank or for fun expect people to be in such shock they don't know how to retaliate. Not to mention, people who do this are normally expecting someone to lash out and by continually walking past you like nothing happened, they already have the advantage of being able to start sprinting away should you try to follow them.
So, if this happened to me and for some reason I wasn't able to fight back, I would definitely call the cops while following the person to make sure they were arrested for assault. Then again, I have my conceal and carry license, so people aren't normally willing to attack someone who is carrying a loaded gun in plain sight.
