'Cause he appeared to go down on the end of a hard jab. A punch certainly did land, and Martinez's legs certainly dipped to a point where he looked to be taking a knee so the ref counted.
For the "knockdown", the ref thought his knee touched the ground. As for the finish, the minute in between rounds was up and then in was stopped. Hence it was a TKO in the 10th round.
If you go over the time limit or a doctor pushed you over, its a TKO not a RTD? Had he stayed under the time limit would it have been an RTD?
