the spy is the 9th playable class in the game, he wears a suit and gloves. his main ability is disguising himself as enemy players and infiltrating the enemy's base or dealing with obstacles other classes cannot handle on their own. he is able to sap engineer building as well. however he comes with some disadvantages.

the spy can still collide with enemy players and engineer buildings even when disguised.
when bumped into or damaged while cloaked he is slightly revealed however not for long.
the spy cannot emote with the g key while disguised as enemy players.
the spy can still be damaged while disguised as enemy players.

1. (mainly if you are a stationary like the engineer or sniper) keep your back against a wall that way spies can't get behind you.
2. (as the sniper) wear the razorback.

1. hit or shoot anybody you feel or think is acting suspicious.
2. enemy spies do not move at the same speed that teammate scouts move at.
3. ask the person you find suspicious to g key emote, if they do not proceed to attack them.
4. (as the pyro) blast your flamethrower around the desired area to check if there are any cloaked spies.

congrats hope this helped. i can't 100% gaurentee that this will drastically improve your skill though.