This research project was designed to understand the influence of excessively restricting ankle range of motion (ROM) on knee injuries, especially non-contact anterior cruciate ligament (ACL) tear. Participating in physical activity without injuries is important to maintain physically active life style and well-being. To prevent ankle injuries, external ankle supports (EAS) are widely used in sport settings by limiting frontal plane ankle ROM; however, the EAS also restricts sagittal plane ankle ROM that could increase the risk of non-contact ACL injury by intensifying the medial knee displacement (MKD) and ground reaction force (GRF). In this research, the effects of external ankle supports (EAS) on landing mechanics were investigated among 19 physically active college-aged females. Two research manuscripts report the results of this research project. The first manuscript investigated the effect of EAS on landing kinematics and kinetics during a drop-jump landing task. The results demonstrated the use of EAS altered the ankle displacement, total MKD, and vertical GRF; however, no relationship was observed between isokinetic plantar flexor strength and landing mechanics. The second manuscript compared the effect of EAS on landing kinematics and kinetics between drop-jump landing and forward-jump landing tasks. The result exhibited the use of EAS similarly affect ankle displacement, knee displacement, peak MKD in drop-jump landing and forward-jump landing tasks. However, the landing tasks affected the posterior GRF differently, and the EAS altered vertical GRF differently in the two landing tasks. Overall, excessively restricted ankle ROM changed the landing kinematics and kinetics, especially MKD and GRF during landing tasks. Our findings indicate that healthcare professionals should use EAS with care because the overly limited ankle ROM could increase the risk of non-contact knee injuries by increased MKD and GRF. Future research should include an examination of the effect of EAS on the magnitude of ACL strain, an assessment of the strength of the other muscles, an evaluation of the muscular activation during a landing task. These studies help understand the landing techniques and strength training to reduce the risk of non-contact ACL tear among physically active population.