How to get Hitmontop in Pokémon GO is a little different from how you would expect. While acquiring a Pokémon through evolving another - in this case, Tyrogue - is not that unusual, Tyrogue has three potential Pokémon depending on their stats.
So what can a Tyrogue evolve into? Well, your Pokémon will either become a Hitmonlee, a Hitmonchan, or a Hitmontop. All three of the potential evolutions are fighting- types, but again, which one you get depends on its highest stats.
How to Get Hitmontop in Pokémon GO
Hopefully, you have managed to get a Tyrogue. If not, hop to it! Otherwise, getting yourself a Hitmontop is going to be a little trickier than you thought. But if you do have Tyrogue, then great!
Evolving your Tyrogue into a Hitmontop can only happen if their stamina/HP stats are the highest ones. Of course, if all the stats are the same then the evolution will be random so your chances dip a bit. If two of the Tyrogue's statistics are the same, then it's a fifty-fifty chance for what evolution you get. If you happen to have a fifty-fifty split with no chance of upping one (such as they're both maxed out) then by all means go ahead if you're happy with the chance of getting a Hitmonlee or Hitmonchan instead. If not, you might be waiting around until you can catch another Tyrogue and trying again.