Final answer:
A positive drawer sign often indicates an injury to the anterior cruciate ligament (ACL), which is consistent with information suggesting that the ACL can be damaged by trauma to the lateral side of the knee.
Step-by-step explanation:
A positive drawer sign in the assessment of a knee injury is indicative of damage to one of the knee's cruciate ligaments.
In the context of a football injury and the details provided, the positive drawer sign most likely indicates an injury to the anterior cruciate ligament (ACL). This is supported by the information indicating that a strong blow to the lateral side of the extended knee can result in a rupture of the ACL, particularly as part of a 'terrible triad' injury which also involves the tibial collateral ligament and the medial meniscus.
Additionally, the ACL is known to support the knee when it is flexed and weight-bearing and is commonly injured through faltering movements such as twisting and hyperextension.