It looks like possible valgus deformity in the left leg. Here is some reading about that:
http://www.thepoultrysite.com/articles/1051/leg-health-in-large-broilers/
https://www.researchgate.net/public..._of_the_Intertarsal_Joint_in_Broiler_Chickens
http://www.thepoultrysite.com/articles/1051/leg-health-in-large-broilers/
https://www.researchgate.net/public..._of_the_Intertarsal_Joint_in_Broiler_Chickens