Those kinds of players appear anywhere.
Recently had a game on irelia, early on by level 3-4 or something my jungle olaf just runs into enemy jungle Taliyah a little bit below baron bit and starts to fight her.....while having 20% less HP than her.
I immediately run down but as olaf facetanked her entire combo and more he ends up dying before i reach her, and with my opponent Riven right behind i only barely kill Taliyah who still had 50% health before dying myself
Bad trade but i had hoped Olaf would at least flash her E and W to avoid some damage (and last longer)....which he didnt.
Then when i hit 7 olaf runs in, lvl 5 and tries to fight Riven (70% health) when im down to 40%, he instantly dies and because i moved a bit to close Riven gapcloses with flash and kills me too.....apparently olaf had been invaded and lost all his camps because he went bot&mid and died without clearing anything.
I later manage to kill the Riven a couple of times bringing us back to a nearly even score of like 4.4,1 and 4,5,0.
Then Olaf runs in again and tries to 1v1 her being 2 levels below her and having like 1 kill and 2 assists, blows up from full health almost right up.
Then the fellow claims it was the laners that lost him the game and that he did everything he could x)
Another game i played Kai´sa and enemy team went on Baron, my Team´s poppy and Amumu decide they wana go in 2v4, rush the Baron pit and jump the enemy jungle yi.
Amumu misses his bandage toss, misses his ult by using it after Yi pressed Q to gapclose on him outside the pit and then he& actually gets used as healing potions by Yi who heals of them with conqueror.
Poppy missed everything as well, then after killing them Yi comfortably goes back and finishes baron.
Later poppy and Amumu run into the Dragon area (just the two of them again) about 10 seconds after the Dragon went down and they find the entire enemy team waiting and die instantly.
They then blame the rest of us for not following them in.....while the rest of us had just revived.
So like......screwball players can come up anywhere at any time, you can only try to adapt as you go.