The stats tell us that Olynyk is an above average to good defender in the NBA.
1. His steal rate is pretty good for a big: 5th among all centers and 3rd among Centers with at least 20 MPG.
2. His defensive plus-minus is solid: 21st among centers and ahead of "defensive-minded" bigs like Robin Lopez, Hassan Whiteside, Dwight Howard, Bismack Biyombo, Steven Adams, John Henson, Kendrick Perkins, Al Horford, and Andre Drummond.
3. The players he guards shoot at a below average rate (
http://stats.nba.com/player/#!/203482/tracking/defense/). Comparitively, players he guards shoot .7% less against him on 3s, .6% less on 2s, and 1.7% less on shots less than 10 feet.
4. His OFG% at the rim is 53%, which is on par with Vucevic, Giannis, Mi Plumlee, West, Garnett, Z Randolph, McGee, Faried, Bass, Milsap, Monroe, and Nowitzki.
5. He is in the 66% of all players in the NBA at defending the pick and roll, 47% at defending spotups, 20% at defending postups, and 14% at defending the isolations.
This compares to Kenneth Faried, who is in the 67% at pick and roll defense, 49% at defending spotups, 20% at defending postups, and 37% at defending isolations.
This shows two things: 1) Olynyk is uniquely fitted to play as a big man in the NBA today. He defends the pick and roll and spotups at an average to above average rate, which is what bigs need to do on defense more and more. 2) Olynyk actually compares in 3 of 4 categories to Nowtizki, Horford, and others too. I think with his IQ and work ethic, he will continue to improve.
6. His foul rate ranks tied for 16th worst in the NBA, but he is a young big, and young bigs normally improve in this over time.
7. His rebounding rate is below average, but it is still on par with Miles Plumlee, Mason Plumlee, Splitter, R Lopez, T Jones, Milsap, Noel, Gibson, Ryan Anderson, Illyasova, Hansbrough, and Motiejunas. This is true even though he spends more time away from the basket than some of these players.
8. His block rate is one of the lowest of centers in the NBA, but is ahead of Asik, Vucevic, Kanter, and Pachulia.
Give me a stat that proves he is a bad defender? I see stats that say he is bad in certain areas, but other stats that say he is good in other areas.
I honestly think this is primarily an issue of his appearance. Because he is a long-haired, goofy-looking guy who moves somewhat awkwardly, we assume is a bad defender. If you actually dig into the little things he does on the court, and stop evaluating defenders based on highlight plays, you find that he is an above average defender in the NBA who is still improving his athleticism and defensive IQ. I want him as a Celtic.
This does not even begin to touch on his offense, where he ranks 8 among centers in assists, 4th among all qualified centers in 3%, 2nd in offensive RPM among centers, and 8th in RPM among centers.