Why burning belt on 48" Craftsman riding mower

Since you mentioned "48-inch riding mower" let's assume your question is about the mower deck and not the overall mower or its main drive belt (if manual shift-on-the-fly model). If the belt burns that means it is running but slipping against something; or that the drive sheave us turning against an impeded belt. In the first case the belt will be burned along its length; in the second the burning will be occuring in one location(s) along the belt. In any case of belt slippage, check first that all tensioners (springs) are properly in place and not broken or fatigued and in need of replacement. The only other thing would be resistance to belt running, such as:
blade blockage; blade rotor resistance from lack of grease or ruined bearing in need of replacment; grass clogging on deck underside or under blade drive pulley on deck top side; a pully sheave out of round; an obstacle between belt and sheave that is preventing free turn of sheave and belt run; misrouted belt; an overstretched belt that cannot be sufficiently tensioned. Inspect and correct or replace as needed.