Another suggestion.
I have a server that is running only fy_maps. Some of these maps the players starts without a knife. You know what happens then if knife arena comes up?
And some maps, for example fy_matrix_duals have a wall between the players at the start. If for example HE-arena is running, you cannot destroy the wall between the players, because they cannot chosse the knife they have.
Suggestion is the following:
Give at every roundstart every player a knife and allow choosing it, no matter what weapon is actually running.