When having 1…n relation between a base object and a list of other object, e.g. when a tournament has a list of players, removing one of the players from the list isn’t as obvious as one might expect.
var t = DB.Tournament.FirstOrDefault(c => c.Id == idTournament);
var g = DB.Golfer.FirstOrDefault(x => x.Id == idGolfer);
This Stack Overflow post fixed this issuse for me.