PG - Marcus Smart (Memphis Grizzlies)
The Utah Jazz are not as desperate for a starting point guard as they were to start the season. Kris Dunn has settled in nicely as the team's starting one, but that doesn't mean that Marcus Smart isn't someone who could reshape the team's defense. Dunn should be playing 25 minutes or more a game, but it really doesn't matter if he starts games. Dunn off the bench as the sixth man could be fantastic.
But you only get there if you have someone like Smart who can provide excellent defense. Smart can do that, and having Dunn come in for him would give the Jazz a brutal one-two punch that you can't truly overcome. Not to mention when the Jazz would opt to run lineups with both men in at the same time. That would easily be the best perimeter defense in the league, at least at the guard position.
He doesn't improve the offense much, and you'd likely have to have someone like Jordan Clarkson in the deal to make the money work, but the offense has been so good with or without Clarkson in the lineup as of late, that whatever you lose with Clarkson won't be so much you can't afford to add Smart.