Overall it looks pretty choppy; here's some notes as I looked at it frame by frame that I think may be causing that:
The head typically never moves left or right in a running animation, so that may be an issue here, and also the vertical movement isn't the same for each leg movement. The first 6 frames seem ok on this point as the head is moving smoothly, but afterward it seems random where the top of the head is and doesn't match how high it was off the ground for the other leg. I guess I'm talking more about the total height of the character, rather than just the head itself.
There's also a lot of body shifting left and right it seems. The torso rotation is ok but his center of gravity is shifting around too much, and should be relatively stable horizontally.
Also you may want to add some more contrast between the (viewer's) front leg and back leg? They can kind of do the optical illusion of switching which one's overlapping the other which doesn't sync up with the correct arm in front.
Lastly for a run, both feet are typically off the ground at their farthest point across, with the front leg's knee bent only slightly, but in these frames your pose isn't as strong as it needs to be making the animation kind of look like an intense power walk instead of a run.