(1) This study examined the impact of fatigue and unanticipated factors on knee biomechanics during sidestep cutting and lateral shuffling in female basketball players, assessing the potential for non-contact anterior cruciate ligament (ACL) injuries. (2) Twenty-four female basketball players underwent fatigue induction and unanticipated change of direction tests, and kinematic and kinetic parameters were collected before and after fatigue with a Vicon motion capture system and Kistler ground reaction force (GRF) sensor. (3) Analysis using two-way repeated-measures ANOVA showed no significant interaction between fatigue and unanticipated factors on joint kinematics and kinetics. Unanticipated conditions significantly increased the knee joint flexion and extension angle (p < 0.01), decreased the knee flexion moment under anticipated conditions, and increased the knee valgus moment after fatigue (p ≤ 0.05). One-dimensional statistical parametric mapping (SPM1d) results indicated significant differences in GRF during sidestep cutting and knee inversion and rotation moments during lateral shuffling post-fatigue. (4) Unanticipated factors had a greater impact on knee load patterns, raising ACL injury risk. Fatigue and unanticipated factors were independent risk factors and should be considered separately in training programs to prevent lower limb injuries.

(1) Background: The pull-up jump shot is a commonly used scoring technique in basketball. This study aimed to investigate the biomechanical effects of knee brace stiffness on knee joint mechanics during the pull-up jump shot in female basketball players and to evaluate the potential risk of non-contact anterior cruciate ligament (ACL) injuries associated with different stiffness levels. (2) Methods: Sixty-six female basketball players performed pull-up jump shot drills while kinematic and kinetic data were collected using a Vicon motion capture system and a Kistler ground reaction force (GRF) plate. (3) Results: A one-way analysis of variance (ANOVA) revealed that both low-stiffness and high-stiffness knee braces significantly reduced knee flexion angles (p = 0.001) but increased indirect contact forces in the sagittal plane (p < 0.01). Notable differences were observed between low-stiffness and high-stiffness braces, as well as between braced and unbraced conditions. However, no significant differences were detected between the effects of low-stiffness and high-stiffness braces. (4) Conclusions: Athletes should select knee braces based on the intensity of competition and training, and those with ACL concerns should opt for high-stiffness knee braces for enhanced joint stability.