It would be useful to know what injuries he sustained, as this impacts on why he may move the way he does. Are there joint restrictions or neurological deficit etc..
Several things spring to mind when watching him walk.
* Is there neurological involvement, as he does not appear to be engaging certain muscles. This may be due to weakness from lack of use or a lack of innervation (nerve supply) to these muscles. There is little evidence of a heel strike to toe off pattern.
* Was there pelvic / lumbar spine involvement as he has poor dissociation of movement, hanging off of certain joints and muscles, rather than engaging others.
* Is there a leg length deficit, his lack of control of the left hip, with deformity at the knee, and apparant lateral rotation of his tibia indicate there could be.

I agree with above comment that he needs to regain pelvic and hip control. You also need to ensure that there is no leg length difference and that joint ranges are as close to normal as possible. If these are reasonable then there appears to be a need to increase knee extension control, as he appears to walk with slightly flexed knees and poor quads control especially on the left (this may also be due to his lack of hip extension). He also looks like he needs to do work on both hip extensors, with attention to glut med on left. He also appears to not use his calf muscles effectively, with increased activity of ant. tibialis muscles and toe extensor.

I think that a useful place to start would be a full neurological, joint and muscle assessment. Kinetic control exercises are excellent for progressing from little control to higher functional control of muscles. Regaining lower level control in non-weightbearing positions would help, as well as graded functional exercises.

I hope this is useful and that I have not missed the mark completely. Ideally it would be better to see him with only shorts on and as mentioned above walking for more than a couple of steps at a time.