It’s hard to imagine, but the weakest Avenger took out the strongest one. More of a ‘mercy kill’ than anything else, Hawkeye took out The Hulk whilst in his Bruce Banner form; like a coward.
Despite some calling it blatantly made to line up with 'Captain America: Civil War', Civil War II is actually quite an interesting story. It essentially revolves around a new Inhuman awakening to their power; the power of kind-of-sort-of seeing the future. The future he saw that led to Banner going the way of Uncle Ben was The Hulk going all Hulk on the Avengers.
Now really, the reason The Hulk was taken out was because, much like in the first Civil War, his presence would be a perpetual trump card. No matter what side he's on has the uncanny ability to plough through foes with little to no resistance, and thus The Hulk had to go. Last time he was sent off to another planet; this time he was shot in the face by Hawkeye.
Banner hadn't turned green in a while, so when the Avengers came to arrest him he was understandably confused and started getting irritated. Hawkeye took a shot, using an arrow specially made by Banner in case he turned Hulk again, and even stood on trial for the act.
Luckily he didn't stay down for long. The Hand (those ninja jerks from the Netflix shows) straight up Frankenstein's-Monster-ed him and made him a zombie samurai, but he was soon freed from this awesome fate.