07/17/2015 08:56 EDT | Updated 07/17/2016 05:59 EDT

Q&A: Swimming guru Byron MacDonald on DQs

CBC Sports spoke with Byron MacDonald, a former Olympian and now the University of Toronto swimming coach and CBC's swimming analyst, about the controversy on Day 6 of the Pan Am Games.

Canadian Emily Overholt and Brazilian Thiago Pereira were each disqualified for non-simultaneous touches in their respective 400m individual medley races. What is a simultaneous touch?

McDonald: What happens in butterfly and breaststroke is that swimmers must touch the wall at the exact same time with both hands. Can you explain why Overholt and Pereira were disqualified?

McDonald: Both swimmers touched slightly, and I mean ever so slightly, one hand before the other hand. That's what's called a non-simultaneous touch. In swimming terms we refer to it as a "patty-cake turn."

We were able to take [footage] and slow it down frame-by-frame, and it was true. A lot of people were thinking that the judges missed it; it was very close and I would argue at times you should give the benefit of the doubt to the swimmer. But when you slowed it down really slow, it was definite that they didn't touch simultaneously.

FINA, the governing body of swimming, will not allow judges to use playback video. Unlike the NFL or NHL, [swim judges] are not allowed to use [replay footage]. The turn judge will write the error on the card and submit it to the head referee. The head referee would then tell the head of the meet to decide if they're disqualified. What happened with the appeal process in one and/or both of these cases?

McDonald: If you want to appeal a disqualification, you cannot be dishonest about what you saw. That is, if they argue that you saw the swimmer do a simultaneous. touch or question the judge's vision. The only grounds you have for appeal is maybe the judge was standing in the wrong place and didn't have the sightline to see the touch properly or that the decision was marked incorrectly on the card.

One of the two judges wrote down that [Pereira] touched with one hand. One could say that that's not really what happened, that they did touch with two but not simultaneously, but if you extrapolate until the end, they obviously did touch as one and then touch with another… That's the argument that they were trying to make to get him reinstated. Is a disqualification in a swimming event a common ocurrance?

McDonald: I was with some former swimmers last night and we were chatting about it and none of us could remember, ever, two gold medalists being disqualified in back-to-back events or even actually in an entire evening, let alone back-to-back events.

We have seen a gold medallist get disqualified, not often, but the very, very odd time it's happened, but I've never seen two in an evening. It was shocking.