Fallout 4 Homerun Achievement / Trophy Guide (How to make a Homerun)
Once you get to Diamond City, you will see the small market in front of you. If you look down you can see the starting point for the homerun on the ground. Turn right run over the other 3 bases around the market.
Make sure to step on all of them so they register and finish at your home base again to unlock the “Make a Homerun” Achievement / Trophy.