Although high picks like Kyrie Irving will most likely end up making the biggest contributions in their career, there is usually a player who will surpass everyone's expectations.
Last year, Landry Fields held that title and this year (assuming the season ever starts), that player could very well be Kawhi Leonard.
First of all, this was a great move for the Spurs. Even though they had to give up George Hill, who would have been Tony Parker's replacement, they gained a lot in Leonard. It's obvious that Richard Jefferson is not working out in San Antonio, which could lead to Kawhi Leonard getting a lot of minutes in his rookie season. He may even find himself starting by the end of the season. His potential is higher than most players in this draft, and his play will definitely make several lottery teams regret passing him up.
On defense, Leonard can possibly play like Luc Richard Mbah A Moute or Shawn Marion, as a versatile defender who can guard multiple positions. He has the length and athleticism to pester low post players, while still having enough speed to keep up with smaller players. Not to mention, he has Tim Duncan to help him if he gets beat off the dribble or overwhelmed by a post player.
Duncan will definitely be an important factor in Leonard's success during his first few years. Knowing an elite defender like Duncan is behind him will let Leonard take more risks on defense, which might lead to a lot of steals. He was a great rebounder in college and rebounding is usually a stat that translates to the NBA since rebounding is mostly about positioning and desire.
On offense, Leonard needs some work, but he has the physical tools to be successful. Everyone knows about his freakishly large hands, which are definitely an asset when it comes to finishing around the rim.
He really needs to work on his outside shot, but he has shown some shooting ability on occasion. He won't put up great offensive numbers right away, but he will be valuable on the glass and the defensive end.
Overall, he can play like a Gerald Wallace or a Scottie Pippen as a guy who can really do everything well. Let's not forget that Scottie Pippen was also drafted for his wingspan and upside, two characteristics that Leonard possesses.
If he continues to polish his game, there's no reason why he can't become a very effective small forward who plays at an almost all-star level in three years.