Deandre Ayton shouldn’t take all the blame for Arizona’s 89-68 first-round loss to Buffalo on Thursday. When a 4-seed loses to a 13-seed by 21, there are systemic issues at play. It wasn’t his fault that he never got on track offensively. His teammates forced bad shots, didn’t space the floor, and couldn’t get the ball inside. The concern when it comes to projecting Ayton in the NBA is what happened on defense. Buffalo didn’t fear the likely no. 1 overall pick in this year’s draft. The Bulls attacked him off the dribble and challenged him at the rim. Buffalo exploited what has been Ayton’s biggest issue since high school, the one NBA scouts and executives will have to grapple with over the next three months: The 19-year-old doesn’t defend as well as a center with his athletic ability should.

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Ayton is the most physically gifted player in the country. Not only was he bigger (7-foot-1 and 260 pounds with a 7-foot-5 wingspan) than everyone he faced this season, he was more explosive, too. Buffalo shouldn’t have had an answer for him. Its starting center, junior Ikenna Smart, is 6-foot-10 and 241 pounds. The Bulls packed the paint and kept two guys on Ayton, but the Wildcats were never able to make them pay for it: Arizona shot 2-of-18 from 3 (11.1 percent), its worst performance all season from behind the arc. The Wildcats’ freshman superstar was essentially handcuffed on offense. The only way for him to affect the game was on defense, and he couldn’t do it.

The Bulls ran an NBA offense. They played four and sometimes five 3-point shooters at a time, spreading out the Arizona defense, and they took advantage of the available driving lanes to get inside. Their shot chart was a thing of beauty: They took only eight midrange shots all game. The Bulls went 15-for-24 in the paint and 15-for-30 from 3. Ayton offered little defensive resistance. He couldn’t keep his man in front of him, and he wasn’t an effective second line of defense. He blocked only one shot.

“Ayton doesn’t have natural shot-blocking instincts. I’ve been saying that for years,” one longtime recruiting analyst texted me after the game. “He might be the first positionless 5 on offense who doesn’t want to be a 5 on defense. He’s so strange.”

Low block numbers are the biggest red flag in Ayton’s statistical profile. They improved over the second half of the season from his historically poor performance in the first nine games, but he still lags far behind his peers. Here’s what the last three big men taken with the no. 1 overall pick did in their only college seasons:

How Does Ayton’s Shot-Blocking Stack Up to Past No. 1 Picks? Player Year Blocks per 40 minutes Player Year Blocks per 40 minutes Anthony Davis 2012 5.8 Greg Oden 2008 4.5 Karl-Anthony Towns 2015 4.3 Deandre Ayton 2018 (projected) 2.6

Blocks, in and of themselves, don’t mean anything. They are important because of what they represent in terms of protecting the rim. A center will alter far more shots than he’ll block in the NBA. Professional guards are bigger, more athletic, and more creative than their collegiate counterparts. Block rates plummet at the next level. Davis is blocking 2.4 shots per 36 minutes of playing time this season, and Towns is at 1.5. Ayton will be declining from a much lower starting point than either.

Ayton has the physical tools to make every defensive play. His one block against Buffalo came when he recovered on junior guard Jeremy Harris, who had beaten him off the dribble, eating up space and pinning his floater off the glass. He shows flashes of incredible defensive potential, but they don’t come often enough. Arizona gave up several baskets Thursday simply because Ayton was not paying attention. While the Wildcats’ perimeter players did a poor job of containing dribble penetration, he should have been able to erase some of their defensive mistakes.

Harris, in particular, tormented Ayton. Ayton played next to one of two traditional big men, seniors Dusan Ristic and Keanu Pinder, so he was forced to match up with Harris, a 6-foot-7 guard whom Buffalo uses as a small-ball 4. Harris took him off the dribble whenever he wanted, and he exploited Ayton’s lack of fundamentals by finishing around him when the big man didn’t keep his hands up around the rim. The coup de grace came late in the second half, when Harris waved away a screen to isolate against Ayton:

Jeremy Harris making number one pick DeAndre Ayton move pic.twitter.com/NbaO0JPmzX — Abdul Memon (@abdulamemon) March 16, 2018

The matchup between Harris and Ayton was a microcosm of the entire game. Buffalo knew something the rest of the country didn’t. Nate Oats, the head coach, spent the past few days insisting that his team wasn’t an underdog. Nor did he act surprised when he had a 40-38 lead at halftime, telling the sideline reporter the Bulls were the better team. Oats told her before the game that “it wasn’t what Ayton could do to us. It was what we could do to him.” He created a game plan under the assumption that Ayton would be a defensive liability.

It’s not like Ayton was playing for a coach who doesn’t know how to install a good defensive scheme. Defense has long been the hallmark of Arizona head coach Sean Miller’s teams. According to Sports-Reference, the Wildcats’ worst defensive rating over the past six seasons was no. 68, despite massive annual personnel turnover. They had the no. 165 defense this season. It has been their Achilles’ heel all year, and it caught up with them. A lot of fluky things can happen in the NCAA tournament, but this game didn’t feel like one of them.

None of this is the end of the world for Ayton’s draft prospects. There’s only so much even an über-talented 19-year-old can do to rescue a program that has been taking on water for months. The Wildcats have been under a cloud since former assistant coach Emanuel “Book” Richardson was indicted by a federal grand jury in November. Ayton has had to deal with even more scrutiny after ESPN reported that Miller had offered an agent $100,000 for him, although the accuracy of that report is in question. It’s a lot to handle, and the Arizona players seem like they had wilted under the pressure by the end of the loss to Buffalo.

Ayton wasn’t put in the best situation on the court, either. Miller played him out of position at power forward all season, and his future NBA coach won’t ask him to defend 6-foot-7 guards like Harris at the 3-point line. However, Jaren Jackson Jr. was dealing with the same positional issues at Michigan State, and he was one of the best defensive players in the country. There’s nothing Jackson can do on a basketball court that Ayton can’t, at least theoretically.

Ayton has an incredibly high floor regardless. He will play in more space in the NBA and have better perimeter players around him. Most NCAA centers have to adjust to bigger and more athletic defenders at the next level. Ayton will have almost as much of a physical advantage as he did in college. He’ll have an immediate impact just from catching and finishing around the rim, as well as posting up smaller centers and demanding double-teams. He can pick apart a double-team, and he can drag his defender all the way out to the 3-point line.

His defense, though, will determine how good his team becomes. A team with a center who doesn’t play any can be only so effective. Arizona found that out Thursday. The worst-case scenario for the team that drafts Ayton is what happened with DeMarcus Cousins, who has never been part of an effective defense in nine seasons in the NBA. Even playing next to Anthony Davis could help him only so much. There’s no reason Ayton can’t become an elite defensive player at the next level, but it would be a lot easier to believe he could if he had been one in college. It will only get harder from here.