This is what I picture when he's reaching for the shoe. He is up on the mat with his right arm extended and he is bracing himself with his left hand on the top of the mat. He keeps trying to reach deeper for the shoe and inserts the upper portion of his body in the mat, still holding on with the left hand. Remember his arm gives him 2-3 more feet of reach. He ends up loosing his grip with his left hand.
He is found with his right arm in front of his face, which is how he would have ended up, if he were reaching for the shoe. His left arm was at his side bent toward the back. That's the position I would expect his left arm to be in, if he lost his grip with his left hand and fell in.
It appears he's in a hurry as he runs across the gym towards the mats in the video. He most likely was rushing to get the shoe also and getting frustrated. He may not have had enough time to go ask for help, or move mats, etc. and all he was focused on was getting to class. Rushing can end up in accidents happening because your not really thinking, your in a hurry.
Now, it can be argued as some have suggested, that as he was reaching for the shoe someone horsing around, pushed him in and just left him there. The video tapes, should have revealed any persons that were in the gym for the minutes that this happened. The investigators have stated they have questioned everyone and verified the whereabouts of the people that the parents suspect.
There are thousands of pages of reports and hours of video. Many, many hours have been put into the investigation. Unless someone admits that they pushed Kendrick in the mat as some have speculated, then I don't see how the parents have a case for murder. I don't see anything that a prosecutor would take to trial.
I don't see all these things that the attorneys and others are stating as having any basis of fact or evidence. I see a lot of emotion and a lot of reaching that is taking away focus from facts and evidence. The accusations of this being a racist crime, a coverup and the flat out naming of minors killing Kendrick, that were found not to be present at the location during that time period, IMO are unfounded.