Hariyama's weakness in Pokemon GO is essential to know when trying to take it down in a raid.
Hariyama is incredibly bulky but can still pack a pretty heavy punch so it's not a good idea to go into a battle with it unprepared. Hariyama, the arm thrust Pokemon, is a Fighting type Pokemon, making it weak to Fairy, Flying, and Psychic type moves and resistant to Rock, Dark, and Bug type moves.
Hariyama Weakness Pokemon GO: How to Defeat the Pokemon
Be careful about using Fairy type Pokemon in this matchup, as Hariyama can use both Bullet Punch and Heavy Slam to punish if you do. Your best bet is using some powerful Psychic or Flying types. Mewtwo and Deoxys are your best options, both having very powerful psychic options.
If you don't have access to either of those two, Espeon and Alakazam are also excellent options. Xatu, Latias, Latios, Lugia, Swoobat, and Sigilyph also have double resistance against Hariyama's attacks as Psychic and Flying types if you want to play a little more defensively.