I still don't see Rosario playing a four. He is the third lightest player on the team (180lbs) and the other two players are 5'11' 170 and 6'2" 175, although Koulibaly is also 180, but four inches shorter.
Rosario has been a 3, at the HS, AAU level. He occasionally played STRETCH 4, because he had the height, at 6-7. But he, they(coaches), could get away with that, because it was HS, AAU, not College.
At the college level, he just doesnt weigh enough to play the 4. At 6-7, 180, he is a stick figure, wiry thin. If you blew on him in the post, he would fall over. He cant post up, and more importantly, he cant defend the post. Any BIG BIG, would have a field day against him.
That said, in extremely limited situations, he can, could theoretically play the 4, once in a super great while, because of his 6-7 height, even at tbe college level.
Rosario really is a Sean Elliot, Malik Sealy, Scottie Pippen(6-6.5-6-7-6-7.5 3,2,4 Spots HYBRID)TYPE(NOT SAYING HE IS GOING TO BE THE NBA PLAYERS THEY WERE). He is a 6-7 180 3,2,4 spots HYBRID, that primarily plays at the 3 spot, can play the 2 spot, and can play the 4 spot.
At the Pac 12 level, he Rosario will PRIMARILY play at the 3 spot, and the only way he would play the 4 spot, and 2 spot, is in garbage time, to help him get minutes on this STACKED Roster.
His 3 spot minutes dont have to come in garbage time however.
He could easily end up as the #2(at best),#3(at average),#4(at worst), back up at the 3 spot, where he could get about 8(At worst) to 17(at best)(as a range), minutes per game(not in garbage time).
He will probably get about 6 ppg. 1,2 rebounds, .5 steal,
He is semi raw, needs some development time.
He was injured last year, which hurt his development, otherwise he would probably have developed similar to Bamba's pace, last season.
His Junior year is where I think Rosario takes off, develops the most, sees the most improvement.
So he is NOT a 4, PF.