As much as Biyombo's ability to alter shots off-ball is great, it's his ability to change them on the ball that was especially impressive. Of the 21 charted defensive post plays for Biyombo on Synergy Sports Technology, he blocked 6-7 shots on the ball and severely altered 3-4 more shots. Nasty. Granted, a limited sample size, but still nasty.
Overall, Biyombo's post defense was stellar this year. On those aforementioned 21 post plays, his opponents managed to shoot just 22% (according to Synergy). Holds his position well, even against veterans, shows good balance and shuffles his feet well. Very sound in his approach.
Also, seems competent guarding outside the painted area. Shows hard on pick/roll and moves his feet well on the perimeter. Can legitimately guard both frontcourt positions. Though, he's not without his flaws defensively. Sometimes loses sight of the ball and has a tendency to over-help.
Biyombo might struggle a little adjusting to defending NBA talent, which is expected of any newcomer. But he will be much more prepared than any college prospects to defend against NBA offenses thanks to his time dealing with the talent and precision of many of the ACB teams.