Clint and Natasha like to play a game they call "Saskatchewan," for reasons that they both claim to have forgotten by now. It's just a Clint-and-Natasha thing.
The point of the game is to try to get the drop on each other. But because they are who they are, sometimes they end up going to ridiculously elaborate lengths to win.
The rest of the Avengers refer to it as anything from "murder tag" to "happy-fun-not-killing-each-other time" (that's Tony's name for it.) None of the other Avengers have figured out yet that the game never actually ends. They're always playing it; it's just some rounds are more obvious than others.
Clint is being lazy today--only climbing through three stories of ductwork in Avengers Tower and then belly-crawling along the drop ceiling to Natasha's room. Nothing compared to the time he sky-dived onto the deck of Tony's yacht, that's for sure. But hey, even master assassins have lazy days, and this is happy-fun-not-killing-each-other-time, not a real assignment after all.
He reaches the correct point in the drop ceiling and freezes in place, listening for any signs of movement in Natasha's bedroom. Everything's quiet, so he lifts one of the ceiling tiles very carefully and drops silently to the floor. Natasha is curled up into a ball on the bed, only her hair visible above the covers. Clint draws breath to say "Saskatchewan!" as loudly and obnoxiously as possible--
--and then there's a blur of motion he barely catches out of his peripheral vision, ducking and rolling out of the way of a roundhouse punch, blocking another strike and feeling his left arm go numb, holy shit this guy is big and fast, Clint's going for his knife and sees the other guy do the same--
The bedside lamp clicks on. Natasha is sitting up in bed, looking rumpled and irritated, but in no way reacting like this guy is a hostile who somehow got into her bedroom. Clint pauses and almost takes a metal fist (what the fuck?) to the face, but Natasha calmly says "stand down" and the fist stops about half an inch away from his nose.
Natasha sighs. "Bucky, this is Clint. Please don't kill him, best friends are hard to replace. Clint, meet Bucky."
Clint gives the guy a suspicious once-over. Big, dark-haired, wearing sweatpants and an unzipped hoodie with no shirt underneath. Clint has never seen this guy before. "Who the hell is Bucky?"
Natasha makes a face that Clint privately calls her "I know classified information that you don't" face. All she says is, "That's a little complicated."
The en-suite bathroom door opens and Steve walks out, rubbing his wet hair with a towel. "Did you say something, Tasha?"
Clint's mouth drops open. Steve freezes and gives him a deer-in-the-headlights look.
The only thing Steve is wearing is a pair of boxer-briefs that are in danger of sliding off his hips. Oh, and? Captain Fucking America has hickeys on his hipbones. They're fading even as Clint stares, of course, but the fact that they were visible at all means that Steve must have been covered with hickeys.
Not incidentally, Clint calls bullshit on those underwear belonging to Steve. He's not a black boxer-briefs kind of guy.
Clint looks from Steve (freshly showered and looking freshly fucked) to Natasha (covered by the sheet, but he's not seeing any sign that she's not naked under there) to Bucky (the guy glares daggers at him but there's no doubt that he's got a serious case of bed-head) and puts the pieces together.
"I'll just be...going then," Clint says, backing toward the door.
"You do that." Natasha looks incredibly smug.
"Nice to see you, Clint." Steve gives an awkward little wave.
Bucky continues to glare.
"Aww, Saskatchewan," Clint says once he closes the door gently behind him. He's going to have to be a lot more careful about playing the game from now on, if only to avoid walking in on anything that Natasha might kill him for interrupting.
Shaking his head, he wanders off in the direction of the kitchen, where hopefully there's coffee. Lots of it.