What I saw:
1-Hocker tried to cut inside BEFORE being fully clear of kessler. He was ahead of kessler but not clear of his stride by any means.
2-Kessler put out an arm and said NO WAY BRO, you are not in front of me (yet) and I am not slowing down to let you in. Stay outside.
3-Hocker slapped Kessler's arm down and went for the inside line.
4-Kessler slowed up, ever so slightly and let Hocker in, but Hocker was right in front of him so Hocker's trailing foot made contact with Kessler's forward foot (or Kesslers forward foot made contact with Hocker's trailing foot ...same thing).
5-Hocker stumbled and slowed and flailed to keep on his feet.
6-His flailing rear foot made another contact with Kessler and now Kessler was left with nowhere to go but to the infield. Hocker, with cat-like reflexes, somehow stayed on his feet and kept moving forward (but I think the episode decreased his chances of placing as he probably was pumping lots of adrenaline for 30 seconds after that.)
7-Kessler probably could have jumped back in at the back of the pack but the competitive aspect of his race was, in fact, over once he was knocked to the infield.