Yan and Sterling were four rounds into their Bantamweight clash when the Russian fighter made the illegal move.
‘No Mercy’ was informed by the referee that Sterling was on the floor, meaning he could not be hit.
But that didn’t stop Yan, who threw a knee which left his American challenger flat on the canvas and all-but knocked out.
After several minutes of treatment, Sterling was deemed unable to continue. Yan was disqualified and lost his belt to his opponent, who was crowned the new Bantamweight champion.