Kershaw is a big man with a lot going for him. His timing is everything - total body timing, total stride plant timing, and so forth. In fact, if every pitcher coming along in age were to develop that sense of .. when this-n-that feels just right, they'd be a way ahead of the average learning curve for this position.
Anyway, Kershaw loads up with a high leg "pump", not a leg "kick" (I'll get to the difference between the two later), he's got his upper body's situated where he can simply DROP his stride leg, then balance his hips and upper body forward, rotate the shoulders and deliver. Kershaw does this delivery phase of his pitching cycle with such force that he can actually spin himself around on the front part of the mound.
(Kershaw warming up)
For Kershaw, this works. He's become accustomed to this "ready-SET UP-go". I see no real problems here. In fact, I give the man credit for knowing when to go and when something isn't all there. In the video posting above, notice when Kershaw pauses just for a second - he looks down to where his stride foot is about to plant. Every developing pitcher should practice that. Also, notice during his bullpen session, Kershaw doesn't feel right with one of his motions ... so he STOPS and regroups.
All in all, Kershaw is one of the best in the business. He pitches healthy, he doesn't rush things, he has excellent follow though, pounds the strike zone like it's the only thing in world to do. Combine all that with his strong body, tremendous concentration and so on - you get a Major League example.
What's the difference between a "leg pump" and a "leg kick". Basically this, a leg pump is just what Kershaw is doing in the video. He pumps his upper body into a state of readiness that pretty much dictates his posture ... PRIOR .. to going forward. Nolan Ryan has somewhat of the same tendencies. A leg "kick" is usually in the same motion as the pitcher's total body is drifting forward, with the front hip usually leading the way. Sometimes the differences can be very, very subtle. However, every pitcher has to feel comfortable with one or the other, and a pitching coach who is knowledgeable of what's-what can make a world of difference to a struggling pitcher in training or in rehab.
Now you're probably asking yourself --- so big deal... one way or the other the pitcher delivers. Not so fast. There are critical body dictates to each style. Believe it or not, when a pitcher has one style that's part of his signature, when things aren't going right, for whatever reason .... missing the strike zone, a pitch just isn't working ... etc., etc., a pitcher will actually go from one type of stride leg action to the other ... leg pump to leg kick, or the other way around. That small alteration is just one of the ways a pitching coach "notices" things to address something is either going or not going well for his pitcher(s).
Did I address your question pdubs?