Side match guns are the ones that are in calibers that aren't legal for main match use, IE: rifle calibers. Examples, 38-55, 30-30, 45-70, 50-70, .22's, etc., you get the picture. Most of these are too powerful for close up targets anyway.
Some side matches are for main match type guns, such as speed pistol, speed rifle( in pistol calibers) ,speed shotgun, and some long range for the pistol caliber guns and revolvers.
Hope this clears it up some for you.........Buck