  As 3-point shooting in the NBA continues to increase, the importance of
perimeter defense has never been greater. Perimeter defenders are often
evaluated by their ability to tightly contest shots, but how exactly does
contesting a jump shot cause a decrease in expected shooting percentage, and
can we use this insight to better assess perimeter defender ability? In this
paper we analyze over 50,000 shot trajectories from the NBA to explain why, in
terms of impact on shot trajectories, shooters tend to miss more when tightly
contested. We present a variety of results derived from this shot trajectory
data. Additionally, pairing trajectory data with features such as defender
height, distance, and contest angle, we are able to evaluate not just perimeter
defenders, but also shooters' resilience to defensive pressure. Utilizing shot
trajectories and corresponding modeled shot-make probabilities, we are able to
create perimeter defensive metrics that are more accurate and less variable
than traditional metrics like opponent field goal percentage.
