The term is a criticism both in and outside of gaming.
In terms of gaming, I hear the term "tryhard" or "try-hard" most commonly in the following context:
When playing in a non-ranked online game mode where one player is accused of playing competitively (as if in a ranked game). Such actions may be frowned upon or not expected for games that offer ranked and more relaxed non-ranked game modes.
It is often a parting-shot or excuse for a loss. For example, player A beats player B, so player B responds by calling player A a "try-hard".
Of course, accusations are easy to make when one player simply loses to another. However, there can be truth in the matter when, for example, a player always uses the "best" loadout, guns, team, strategies, perks, character etc (depending on the game) in non-ranked games.
I don't really hear it in ranked games, but I guess the same principles could still apply. In ranked games, it can also mean that the player can only win with the best loadout/setup, and is therefore more of a taunt (in the hope that loadout/setup is changed).
I have heard the term in several Street Fighter titles, Call of Duty (of course) and Dota. I haven't heard it in FIFA, surprisingly. Regardless, the meaning seems pretty universal across different games.
I would suggest the following definitions, but these are based on my own experiences:
someone who is perceived to doing all they can to win
"you won because you are a tryhard"
"what a tryhard!"
perceived to only want to win
"he is a tryhard player"
"that is such a tryhard loadout"
In gaming the term doesn't appear to be used in the same manner as the general term. Outside gaming it is used to describe someone who tries harder than required.
This definition is found in the English Wiktionary:
(derogatory) A person usually of little talent who tries hard, especially through imitation, to succeed, usually to gain fame or popularity.
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