While the differences between lower levels of basketball and the NBA are significant in every facet of the sport, they make a larger difference in terms of evaluating defense even though offense actually garners more of the attention. The prevalence of zone defenses, overuse of big men, insufficient floor spacing and less off-ball activity means that just about every prospect spends their entire college career in a significantly different role than they will be asked to do in the NBA. Those factors make it challenging but not impossible to evaluate draft prospects while also providing a solid place to start by weakening the overall sample.
Since film and stats can only provide vague answers on defense, the best starting point is a prospect’s physical tools even though those are only part of the picture. I prefer to focus on a player’s functional height rather than their listed stature, which is a mix of wingspan, standing reach and execution/body control with a splash of vertical leap for the big man positions. The basic idea of functional height is what opposing offensive players will see and feel when that prospect is in front of them and the same thought process is true for weight and strength as many defenders do not maximize their physical gifts on that end of the floor, from big men and help defenders failing to properly use verticality to stronger players who rarely get in the way of opponent drives.
While it can be useful in a variety of ways, physical capability often ends up focusing on identifying outliers in either direction. Prospects who are too small or thin for their position can succeed but likely require more intense scrutiny and there are also circumstances where functional size dictates a position change and the resulting adjustments for the prospect and evaluators alike.
The next step is a logical one: from functional size to mobility. Lateral movement matters at every position in the modern NBA, especially since the combination of footwork and foot speed often serves as the strongest indicator of whether a big man will be able to function as a switch defender. It is even more important for perimeter players as they will have to navigate a complicated mess of screens, cuts and handoffs where moving side-to-side matters much more than straight line speed. Big men deal with the related question of their first and second jump. This is far more than simply vertical leap, especially since the second jump matters so much for rebounding and shot blocking purposes. It is good to look at what kind of load-up a prospect needs and whether he is able to get above other players for rebounds, even more so if he starts in inferior position. The big-heavy nature of current college basketball makes it harder to evaluate but the film is still there and players like John Collins whose rebounding largely translated to the next level.
From there, focus turns to the mental side of defense. It can be harder to piece together since some coaches run schemes that put their players in strange situations but a great place to start is whether a player is engaged mentally and responding properly to what happens on the court. For example, keep an eye on when a player leaves his man to help, especially if his cover is a good shooter. Similarly, prospects who are intelligent and proactive defensively stand out in college and while that is far from a guarantee of NBA success it can be a strong sign in the right direction. While slightly separate from recognition, communication can be hard to discern on film but strong or weak communication can often be inferred with enough examples.
An area that connects the different components of the mental side is positioning and leaking out on rebounds since it combines instincts, recognition and effort. Big men have more reliable responsibilities in terms of boxing out and securing rebounds while perimeter players have substantially more judgment on each possession as they can be opportunistic rebounders on both ends of the floor or become the spark for a transition chance. Players who can override the game plan in unusual circumstances for good reasons are immensely valuable because they can often anticipate in other facets of the game and make life easier on their teammates.
The final component may actually be the easiest to analyze for experts and fans alike: effort. There are certainly times when prospects are justified to take it easy but a player’s motor can be a major indicator of their success at the next level whether they are physically gifted or not. NBA basketball asks so much more of players due to the vastly superior athleticism, skill and coaching that almost everyone cannot afford to skate by too often. Sometimes effort and execution can be confused for one another but watching enough film should make it pretty clear. Getting back in transition instead of complaining about a call, recovering to get back in a play after being beaten or hedging and returning to the roll man are all effort-based defensive actions that can swing possessions and thus a game. There have been prospects who have flipped the effort switch when jumping to the pros, with Ben Simmons serving as a prominent recent example, but those are the exception rather than the rule. One element to keep in mind to avoid overreacting to a player who seems too floaty is their workload, as some college coaches give stars too many minutes often on top of ambitious offensive responsibilities. In those circumstances, it is best to be skeptical but uncertain since the shift to the NBA may alleviate those concerns but that contention is a risky one considering the stakes. As always, context is key.
Those central elements of functional size, mobility, execution, recognition and effort will sometimes lead analysts of all experience and success to eventually incorrect conclusions, but they provide the best chance for getting predictions right when comparing between dramatically different levels of basketball.