With nearly two years of NBA experience under his belt, Luka Doncic has already surpassed a lot of markers many had for him entering the league. He's also hitting milestones not many expected him to reach so early in his career. The Dallas Mavericks phenom has already been named an All-Star starter, been in the MVP conversation and helped pull his team back into the playoff race for the first time in three seasons. In his second year in the league, he's averaging 28.7 points, 9.3 rebounds and 8.7 assists, and arguably has the best second season of any player ever.

His offensive game is already at a point where any improvements that he would need to make are just nitpicking. Yes, he often makes outlandish passes that in the grand scheme of things wasn't the greatest idea, but you can live with that because of his other-worldly court vision that often pays off. His 3-point shooting isn't the most efficient, but you still can't leave him open from beyond the arc because he can have games where he goes 8-for-12 from deep. Offensively, there's still room to improve, but given where he's at as a 21-year-old, some of it you just chalk up to lack of experience.

Defensively, though, is where Doncic stands to improve the most. He's not a complete liability on that end of the floor as many expected him to be, because his size allows him to front bigger players in the post, and he has good enough instincts to come away with steals against guards who underestimate his defensive presence. However, there are areas on defense where he is lacking significantly, and if he improved, it would make his game even more complete. The first area being his closeouts.

This is perhaps the biggest area where Doncic can improve on defense. Too often is Doncic caught haphazardly trying to closeout on opponents before they either pull up for a jumper or drive past him to the basket. He needs to practice better mechanics so he's not giving up as many open shots or easy buckets at the rim.

When he's closing out, Doncic often appears like he's caught off guard. That results in him not being in a good defensive stance, and because he doesn't have the best lateral quickness, he's susceptible to giving the opposing player an open lane to the basket:

His lack of defensive awareness also makes him slow to get to the player to contest the shot adequately:

Doncic will likely never become an elite defender in the league, and some of his lapses on that end of the floor could be attributed to him not trying to exert too much energy on defense given how much the Mavericks rely on him offensively. Still, though, there are adjustments he could make so he's not hindering the team as much.

Take this play against the Sacramento Kings, for instance. Instead of trying to go for a steal that he likely wouldn't have gotten, Doncic should've ran out quickly to closeout on Cory Joseph and deny him an open lane to the rim. Instead, he slowly tip-toes out to Joseph, and before he's even within arm's reach, Joseph is already accelerating to the basket:

There's so many clips of Doncic using poor footwork to closeout on defense, leaving an open lane while closing out, or when he does get there in time he doesn't get a hand up to contest the shot:

Doncic's slow timing as a defender is part of a larger issue for him on that end of the floor. He struggles with switches and rotations, which often leads to open shots. This is something that Doncic could naturally get better at as he progresses in his career, but he'll need to put in the effort and stay committed to working on it. Otherwise, he'll always be a below-average defender.

This also doesn't entirely fall on Doncic's shoulders, either. As a team, the Mavericks rank 17th in the league in defensive rating (110.0), and have lapses where several players on the court fail to communicate switches, making their defense very porous. However, despite the fact that Doncic is still so young, he is one of the leaders on this team, and if he's communicating more on defense, being more aware when rotating and not getting stuck on screens, it could have a positive effect on the rest of Dallas' defense.

A lot of the times, though, it's just Doncic losing track of his man and running into a screen, giving the opponent a wide open look:

Or he's paying too much attention to the ball handler instead of the person he's guarding:

In that play against New Orleans, he doesn't recognize the fact that Nico Melli is setting a screen for JJ Redick, which completely blocks Tim Hardaway Jr. from getting to him. Since Doncic was paying more attention to Jrue Holiday with the ball, Redick is able to get rid of Doncic easily to get a wide open shot. If Doncic would've stayed connected to Redick, he would've been able to get back to contest that shot.

These aren't huge improvements that will be challenging for Doncic to get a handle on, in fact, there are instances where he is locked in on defense and makes a good play. He's been a good defender when he's guarding the ball, and his size does make it difficult for guards to get around him. However, it's all the off-ball work where he needs some help. Positioning himself better when he's closing out, not losing sight of who he's guarding, calling out switches and rotating appropriately.

It's not that Doncic needs to become a world-class defender, but he can become a good one by improving those aspects of his game. Dallas is going to be a playoff-contending team for years to come with him and Kristaps Porzingis, and when the postseason rolls around, Doncic can't be absent-minded on defense. If he puts in consistent effort on that end of the floor, not only will it help the Mavericks defense, but he'll become a more complete player, capable of being a genius on offense and reliable on defense.