Watson actually suffered an LCL tear and bone bruise that you hear little about in a Nov 15, 2014 game. An MRI revealed the aforementioned findings, and an ACL tear was not present at that time. It wasn't until several days later that he tore his ACL (non contact) in practice, a diagnosis which was confirmed by another MRI.
Empirical knee injury risk can sometimes be lessened by strengthening of the muscles that contribute to the stability of the knee through its tendinous attachments around the joint..........the quads and hamstrings. Also attaining the proper balance of these muscles becomes very important. In addition, addressing any hip joint deformity and/or hip joint associated muscular imbalance is very important, in that, for example, the simple turning in of the hip places inordinate stresses on the knee joint.
When you look at skinny legs/knees, muscle "bulking" does not occur around the joint and does not in this way add to any protection of the knee joint (see figure below). Ligaments themselves which act as movement limiters of abnormal joint movement (such as side-to-side or front-to-back) cannot themselves be strengthened all that much with exercise, especially when genetically small/narrow.
Skinny legs/knees have a lesser platform to maintain knee stability. The wider the area of joint bone contact, the less likely they are to fulcrum tilt from one side to another (see figure above), and logically less likely to stress/tear supporting ligaments.