The terms of the scholarship probably say something about participating as required in school activities - comitment to sports fixtures etc. However most schools are reasonable about it and if its not a major fixture & the school are given notice then they would be fine about it .
It seems that the teacher has been unreasonable in two ways:
waiting until today to speak to your son
speaking in such a threatening manner
I would contact the Headmaster directly. Rather than making an outright complaint about the teacher I would couch it it terms of how worried you are about what was said regarding thge scholarship but that it was too late in the day to change your plans... That way you head off any action being taken without your knowledge & bring the behaviour of the teacher to the notice of the Head without appearing adversarial. Hopefully he will have a quiet word with the teacher and you can clarify the situation regarding attendence at sports fixtures so everyone knows where they stand.
DSs school have a fixture list available on-line each term so parents can check dates of matches in advance - maybe you could ask whether this is provided (or sent home in paper form) so you can avoid future clashes/ provide early written notification to the school of any unaviodable clashes in the future.
Not suggesting that you or your DS are at fault - but taking a conciliatory approach & suggesting positive steps will probably be more productive than getting cross (which I would be quite tempted by given the way Ds was treated!)
I hope it doesn't spoil the weekend of treats