Dos'Santos, T, Thomas, C, Comfort, P, and Jones, PA. Biomechanical effects of a 6-week change of direction speed and technique modification intervention: implications for change of direction side step performance. J Strength Cond Res XX(X): 000–000, 2020—The aim of this study was to evaluate the biomechanical effects of change of direction (COD) speed and technique modification training on COD performance (completion time, ground contact time [GCT], and exit velocity) during 45° (CUT45) and 90° (CUT90) side step cutting. A nonrandomized, controlled 6-week intervention study was administrated. Fifteen male, multidirectional, sport athletes (age, 23.5 ± 5.2 years; height, 1.80 ± 0.05 m; mass, 81.6 ± 11.4 kg) formed the intervention group (IG) who participated in two 30-minute COD speed and technique modification sessions per week, whereas 12 male, multidirectional, sport athletes (age, 22.2 ± 5.0 years; height, 1.76 ± 0.08 m; mass, 72.7 ± 12.4 kg) formed the control group (CG) and continued their normal training. All subjects performed 6 trials of the CUT45 and CUT90 task whereby pre-to-post intervention changes in lower-limb and trunk kinetics and kinematics were evaluated using 3-dimensional motion and ground reaction force analyses. Two-way mixed analysis of variances revealed significant main effects for time (pre-to-post changes) for CUT45 completion time, exit velocity, and CUT90 completion time (p ≤ 0.045; η2 = 0.152–0.539), and significant interaction effects of time and group were observed for CUT45 completion time, GCT, exit velocity, and CUT90 completion time (p ≤ 0.010; η2 = 0.239–0.483), with the IG displaying superior performance postintervention compared with the CG (p ≤ 0.109; g = 0.83–1.35). Improvements in cutting performance were moderately to very largely associated (p ≤ 0.078; r or ρ = 0.469–0.846) with increased velocity profiles, increased propulsive forces over shorter GCTs, and decreased knee flexion. Change of direction speed and technique modification is a simple, effective training method requiring minimal equipment that can enhance COD performance, which practitioners should consider incorporating into their pitch- or court-based training programs.