So here's a fun fact: Half-court basketball is practically the only sport Mormon missionaries are allowed to play, so they take it pretty seriously (see: Church Ball).
And when you take something seriously, you get pretty good at it, as these backyard ball player soon found out.
But it's not all fun and games.
As one returned missionary explains: "We used to challenge people to pick up games of basketball/soccer and if we won we got to teach them a discussion. Good times hustlin."
UPDATE: For the curious, here's the full Missionary Handbook, which is filled with other fun gems such as, "If you play basketball, volleyball, or another sport, do not allow the situation to become intense or competitive. (For example, do not keep score.)"
UPDATE 2: Here's some additional context from the description of the original uploader's video:
My cousin Cole, a missionary in Dallas Texas, has been dying to play some street ball and got the chance. After playing it cool asking to play because they are "Just some white boys", they were allowed to play and tried to make it look like they weren't that good. That is until they started to play. [...]
Best part of the story is that one of the guys daughters ended up getting Baptized.