Adding to the list of problems with the CS2 3rd person animations, some movement inputs can cause these broken leg clipping animations.
Using a combination of W+D into an A key strafe, you can replicate the animations in the video pretty easily. This results in ultra jarring and physically impossible leg movements that can create an illusion of instant acceleration, making tracking and predicting enemies extremely difficult (especially when enemies have pistols or SMGs).
In CSGO the leg animation logic avoided these cross-legged movements upon acceleration with much better leg Collison/clipping and more natural looking movement. CSGO 3rd person models also had key visual indicators that made tracking enemy movement intuitive such as upright posture when strafing and counter-strafe animations (indicating strafe direction changes – https://www.reddit.com/r/GlobalOffensive/comments/1ozif10/missing_3rd_person_counterstrafe_animation_makes/ )