Jabari Smith Jr who is an excellent shooting big and good defender.
Two parts - Jabari as a big + Jabari in general
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Part OneI always find the descriptions of Jabari interesting. The description of him as a big ...
Why is Jabari a big and Tatum not a big?
* Tatum has averaged 8-9rpg in the regular season in his previous 4 seasons and 9.7-11.5rpg in the playoffs. Jabari has one season of 8rpg and 3 seasons of just 7rpg. Tatum is a far better rebounder than Jabari.
* Jabari is an above average defensive PF but so is Tatum. If anything, Tatum is better defensively than Jabari. Jabari might be a bit quicker side to side but Tatum is far smarter as a team defender.
* Jabari has two inches on Tatum. Jabari is 6-10. Tatum is 6-8. Similar length. Similar weight / strength. If anything, Tatum is the stronger of the two of them.
* Neither guy has the size to effectively play at center or to be main rim protector / shot blocker. Both are out and out forwards. Jabari a PF/SF. Tatum a combo forward also arguably a PF/SF or a SF/PF depending on which position you think he is best at. Jabari clearly better at PF than SF due to his offensive limitations skills-wise.
I always find that description of Jabari as a big interesting. He can't play center. He gets outmuscled. He gets outmuscled defensively. He gets outmuscled and out-rebounded. Tatum can better battle centers on the boards than Jabari can. Jabari provides little to no rim protection. He has averaged 0.7-0.9bpg in each of his 4 years. He doesn't organize a defense. He just takes care of his own assignment. He is much more comfortable defensively out on the perimeter sliding his feet than banging in the paint. He is a solid but unexceptional team defender. Tatum a better team defender no doubt. Jabari is not a player who can play center. He is more comfortable as a forward. A big forward rather than small forward.
So what makes Jabari as a big and Tatum not a big? He can't rebound as well as Tatum. He doesn't protect the basket better than Tatum. He doesn't physically battle in the paint against bigger bodies any better than Tatum. He is not a better shot blocker than Tatum. He is slightly taller - that's it.
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Part TwoThe main reason Jabari struggles at small forward are the limitations in his skill level. He is a non-passer. A limited ball-handler. He struggles to create his own offense one-on-one unless you give an iso in the mid-post where he can make a 1-2 dribble move out of a face up or post up situation. His shooting is average.
More on the shooting. Jabari has shot around 36% on 3s in each of the last 3 seasons. He takes solid volume at 5.5 threes per game in 32mpg over those 3 years. About half his shots are threes.
He rarely to the foul line (2.5 FTA) despite his size & athleticism because he is a basic spot up shooter or a basic line drive attack the rim threat. His handle is too limited to get him in dangerous areas otherwise. He is a basic offensive player. That is enough for him at PF (albeit still below average for a starting PF and only average for a rotation caliber PF [starters + bench PFs]) but not enough for a SF. That is why he needs to play PF.
He doesn't shoot many midrange jump-shots. He doesn't like to shoot off a dribble drive. Either shoot the 3, straight line drive to the rim, or drive, see traffic and move the ball. When he does shoot the midrange, he is more comfortable out of isos from about 14-17 feet.
My point here is that Jabari has a lot of limitations offensively. He is 4 years into his career and shown little progress in most of them. No progress in his jump-shooting. No progress in ball-handling. No progress in his passing. No progress in his shot-creation except for those clear play calls where he gets an iso at 14-17 feet - he has shown progress there. With so many limitations offensively, it is hard to see much upside there. He looks more like a 4th/5th option than a guy who can ever be a main offensive threat for you.
Jabari is not a cerebral offensive player. He doesn't have good feel for the game. Nor does he have the skills. Jabari is an above average defender but not a great defender. He is no Draymond Green. Nor is he anything more than an average rebounder.
Therefore, a solid two-way starting PF. A guy who can play some SF thanks to his athleticism & defensive versatility but not a lot due to his offensive limitations. Nor can he play C. He lacks the size (bulk) to play C and doesn't anchor a defense / protect the rim well enough to play there for long stretches.