Dos'Santos, T, Thomas, C, Jones, PA, and Comfort, P. Assessing asymmetries in change of direction speed performance; application of change of direction deficit. J Strength Cond Res 33(11): 2953-2961, 2019-The aims of this study were to quantify asymmetries in change of direction (COD) performance using completion time and COD deficit, and determine its influence on asymmetry profiling of COD ability. A secondary aim was to evaluate the relationship between linear speed, 505 time, and COD deficit. Forty-three youth netball athletes (age: 15.4 ± 1.1 years, height: 1.71 ± 0.06 m, and mass: 63.3 ± 6.6 kg) performed the 505 for both left and right limbs and a 10-m sprint test. Asymmetries in 505 completion time and COD deficit were quantified for dominant (D) (faster) and nondominant (ND) (slower) directions. Paired sample t tests revealed significant differences between D and ND directions for 505 time and COD deficit (p < 0.0001, g = -0.53 to -0.60). Substantially greater asymmetries for COD deficit were observed compared with 505 time (p < 0.0001, g = 1.03). Only 2 subjects displayed an asymmetry ≥10% based on 505 times. Conversely, based on COD deficit, 21 subjects demonstrated asymmetries ≥10%. Large significant associations were observed between 505 time and COD deficit (r = 0.500-0.593, p ≤ 0.002). Large significant inverse associations were demonstrated between 10-m sprint time and COD deficit (r = -0.539 to -0.633, p ≤ 0.001), indicating that faster athletes had longer COD deficits. Nine subjects were classified differently for COD ability when comparing standardized scores for 505 time vs. COD deficit. Quantification of asymmetries in COD ability should be based on COD deficits; inspection of 505 times only could lead to misinterpretations of an athlete's COD symmetry and COD ability. Faster youth netball athletes demonstrate longer COD deficits; thus, researchers and practitioners are encouraged to improve their youth netball athletes' ability to rapidly decelerate, change direction, and reaccelerate from 180° turns.