Apparently a back-formation from inting, which is a shortening of intentional / intentionally feeding.
Meanings
(intransitive) To die intentionally in a match by having oneself slain by enemy characters or structures so as to give resources to the opposing team
2017 The difficulty in banning the ‘most toxic League of Legends player in North America’
Tyler’s signature crime was his habit of intentionally feeding or “inting” in ranked matches.
2018 Riot Games Comments on Intentional Feeding Sion Strategy
Inting, or intentional feeding, is one of the greatest sins in League of Legends. This strategy, apparently discovered by a player named MidLanerFromHell, uses Sion as a turret destroyer above all else, even sacrificing himself in the name of base destruction.
2019 Broxah reported Febiven for inting on stream
(intransitive) To make a bad play, even if it's unintentional.
Sorry guys, I inted. I thought I could get the kill and then get out.
(transitive) To ruin a match or a specific part of a match by intentionally or unintentionally dying or making bad plays
I know this guy. He recently inted my diamond promos (promotional games to the diamond tier).
Why are you inting my lane?
(transitive) To make someone lose a match by (mostly) intentionally or unintentionally dying