A second, give or take, at the start of each match where you are unable to
execute the "play the turnframes" command (Keyboard key: Space).
This will hopefully prevent most of the accidental "spacing".
Also an enable/disable hotkey for what I suggested in case you're playing a mod that
requires such sort of actions.

I agree with this idea. I think after you have locked in, that could could press space again to edit your tori. I don't know how many times I've pressed space to go to the next fight and my face gets scrapped of onto the floor by an afk breaker. Although I think you should only be able to unlock then re-lock one. Because holding spaced or rapidly pressing it to re-lock and lock instantly could be distracting.

This is a good idea, although instead of this, there could be a timer when the match is done.

Countdown kinda thing until the match automatically starts with the new player. And if the other player has already pressed space then it would show up as something like "Other player is ready".

Because it does become annoying when both press space at almost the same time or someone does the /spec command in the middle of the fight, where it would be nice to have the space button disabled for a second or longer btw.

Edit:

I'm giving this a edit to be a bit more clear with what I'm talking about. If both press space at almost the same time before a match starts, one of the players will start with everything "relaxed" accidentally, well maybe that requires a double tap of space, I'm not sure. But it would require a timer in my opinion, because if you press space at the same time the match starts, you start with everything relaxed and there's no going back from such an accident. There is no *undo* button for pressing space, that wouldn't help much either if the other player press space before you can undo it. So a timer would be very nice.

And like McDill said, it would be nice to have a one second cooldown for pressing space immediately when the next match starts, mostly for those times when someone is AFK or types in the command /spec for whatever reason without a warning, although that wouldn't be the start of the match. So having that (space button disabled) for a second would be best fitting when someone is AFK "set to spec" or does the /spec command in the middle of the fight.

I agree with your suggestion but, like Irimuru said, I think a mandatory countdown to the next match would be more effective. The countdown would start once both players press space. 3 seconds would be good enough.

Not only would it prevent accidental 'spacing' during the first turn, but it would also counter the glitch where the server 'auto-starts' the next match and give people a small timeframe to save replays if they wanted to.

Yes 3 seconds would be perfect.

3 ... 2 ... 1 ... FIGHT! *Match starts like normal*

Edit:

Although for the replay saving, I guess 3 seconds wouldn't be enough, but I guess the match shouldn't start unless both players are "ready" - In that way you would have enough time to save the replay. Although if you are spectating then that's another problem, because then you're not the one controlling the time between saving the replays.

So maybe there should be a way to save the replay while spectating, even though the next match started already.

Perhaps saving a replay should save not the current fight, but rather the last fight that finished? This way, the players each have the whole next fight to save the replay. This would, of course, require the replay data to be saved by the server longer, but I don't think that would be too much of a strain on the servers.

That would be mighty convenient, far too many times have I lost great replays.
And when I save the replay with the match ongoing, I'll risk a ragequit from the other end.

This is a very good idea, although, then if you are playing, you would sacrifice precious time if you want to save the "previous" replay while in a fight.

I think it would be better that it does record the current fight, but when the next fight starts it would still remain as a recording until that match is finished.

That way you would be able to save the replay before playing, and you would be able to save it at any time while spectating the next match.

But there is also another glitch or something, in which the next match starts when the new player is ready, which doesn't give you any time to save the replay at all.

So for that, there has to be a 2 way confirmation that they are both ready before the match starts, then it would all work out.