Riot. How do you catch the people who decide to troll during the mid game and onward?

I just had a Reksai last game who seemed to be okay. They ganked in the early game, never said a word but was doing well regardless. Laning phase goes somewhat smoothly, I win my lane, top wins their lane, mid lane is at a stalemate. So its what ever.

It felt like this would snowball into a victory. Trist had items, I had Zekes, and Riven pretty much went uncontested at top lane. So Laning phase is done and now we want to group and start trying to work towards our win. But what happens instead? The Reksai suddenly stops helping out. Literally chooses to ignore everything around him and just jungle non stop. We're having a teamfight to defend our mid tower? He's over at wolves, killing them and ignoring the teamfight entirely that he could have easily joined and won. Instead we lose because we don't have a full front line now. Now trist, Lux, riven, and I are pretty upset.

Our jungler, the tank of our team, suddenly just starts spamming surrender and refuses to do anything other than kill camps. When questioned why he was doing this, he said nothing. Of course, since it was a ranked game, everyone else voted no. Noone wants to surrender a game that they were winning, especially a ranked game.Eventually, we lose. We just couldn't stop an elise,thresh,maph,jinx, and Leblanc 4 v 5 with out a tank to protect us.

The game finally ends and guess what? The reksai tells the enemy team gg.

Do you catch people like this, Riot? The trolls who act like they're a decent person early on, then just suddenly does everything they can to avoid helping their team win? They wouldn't ward, they wouldn't clear wards even after getting the oracles form raptor, and he wouldn't help in teamfights for some unknown reason. He says nothing all game, except gg when we finally lose.

So of course, everyone is pretty much pissed now. A seemingly won game became a drawn out loss because ONE person decided they couldn't be arsed to do anything any more. Noone took his buffs, noone denied him his camps. People just say the usually "gj" when he did a nice gank for their lane.

Its baffling and makes me salty that I lost a game because of someone like this. Anyone else have experiences like this? And do you catch people like this, Riot? Because its pretty annoying when it happens. Losing because I'm bad is one thing, but I can still learn from that lost. Losing because of a troll is something entirely different. I don't get to learn anything from it. My team didn't misplay, they just got cheated because our main front line decided that we should all lose.