A handshake? What is a handshake? I doubt very much that more than a handful of footballers have the first idea.
It goes back to the days when, in order to kill someone, you needed to get close enough to plunge something sharp into them.
A handshake, with the most commonly used hand, the right, was an open palm which contained no dagger. It removed suspicion.
Which means that a handshake was not originally a comment on the past but a statement about the future. I do not intend to kill you. The crisis will subside from this point onwards.
Pretty soon afterwards, or perhaps even in parallel, it became a recognised sign of finalising a deal - let's shake on it.
But in essence one does not have to have resolved the past in order to shake a hand. The errors of the past still need reconciliation but the handshake offer is my intention to do nothing to make matters worse.
So, a refusal to shake hands actually escalates. By not agreeing to stop making matters worse you contribute to making matters worse.
I almost understand the problems with the handshake between sparky managers (pun intended) at the end of a heated game. Most problems of this nature are sorted over a drink later. But before the game? Not for the first time I think some players need to grow up.