There is no doubt that Pitino likes to play an up-tempo style where his guards really get out and pressure. With that they take a lot of chances on the defensive end, deny passing lanes, attack the ball, and because of that they give up some straight line drives to the rim.
What makes that possible and effective is having a dominant rim protector on the back end of the defense. Louisville last year had Gorgui Dieng protecting things in the paint and erasing shots with his length, athleticism, and timing.
Now Louisville has someone who looks like he could be Dieng's replacement in that role with Onuaku. Onuaku, who is the younger brother of former Syracuse standout Arinze Onuaku, is someone who has excelled both during high school and AAU as a shot blocker.
Though he is a little slender, Onuaku is a legit 6-foot-10 and has extremely long arms. Those long arms allow him to really be someone who bothers offensive players who try to score over him.
Running with DC Assault, Onuaku completely took over games with his shot blocking. He has that natural timing to block shots combined with being a good athlete and someone who has the previously mentioned length. Also Onuaku is someone who knows his role and takes it on well. He doesn't take himself out of position trying to block everything, instead he blocks shots both his man takes and from the weak side while maintaining his defensive and rebounding responsibilities.
Along with being a shot blocker, Onuaku is also an elite rebounder. This is important because Pitino has always preached and thrived on a physical brand of basketball. Despite not being super strong, Onuaku has a very good motor and that sense for where and how the ball is going to come off of the rim.
His long arms allow him to rebound out of his area, and then on balls in his area he is good at blocking out and making good physical plays to ensure the rebound. Also his hands are fairly reliable so everything he can get to he controls, from there he is a good outlet passer who knows if he gets the ball out quick, he is likely to get rewarded by running the floor and putting pressure on the defense.
Overall Onuaku is exactly what Louisville was looking for in this class. He fills the role of the departed Dieng, and with so many offensive weapons already on the roster, Louisville can mask his deficiencies well.