Intentionally AFK.

instead of thanking your adc for not wanting to put your team at a disadvantage and potentially lose you the game, you want to report him?

To answer your question, you can report anyone for anything. It will be handled by LeaveBuster and that person will get a leaver regardless whether you report or not.

He willingly took a Leaverbuster penalty rather than putting his teammates at a disadvantage. Doesn't seem worth reporting to me.

Looks like they wanted to save their team some trouble and did it so you could remake and move on without a loss. If the person has a pattern of leaving games, Leaverbuster will take care of it.

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So my ADC got the wrong runes and intentionally went AFK to force a remake, reportable?

Well yes, as AFK for any reason is against the summoner code (always try! Chin up!) however ethically I would not. Its the same line as someone dodging because 2/5 of our team have a 20% winrate... dodges are annoying but by god if I could give BE or OE to peep who take that LP loss for themselves rather then all of us I would

Why is this being downvoted?