here is the verage from SWA
Golf bag in hard-sided golf bag carrying case provided by Passenger, including clubs, balls, and shoes. Hooded golf bags or golf bags in a soft-sided carrying case provided by the Passenger will be conditionally accepted.
Note: Overweight charges will apply to golf bags exceeding 50 pounds.
Conditional Acceptance
Carrier may, at its sole discretion, but is not obligated to, conditionally accept the following categories of items for Carriage as Checked Baggage subject to the Passengers assumption of risk for damage to or destruction of such items. Checking items in the condition described below is considered by Carrier as Passengers agreement to this assumption of risk.
(1) Fragile or perishable items
(2) Previously damaged items
(3) Improperly or over-packed Baggage
(4) Soft-sided cases or unprotected/unpacked items
They mean that if you use a soft case they can not guarantee they won't get damaged.