Snow ski equipment, including skis or snowboards, ski boots, and ski poles. Effective March 1, 2012: including one pair of skis or one snowboard, one set of poles, and one pair of ski/snowboard boots encased in a container(s) acceptable to Carrier. When substituting ski equipment for a free bag, Southwest Airlines allows up to two bags (containing one set of snow skis, ski poles, and ski boots) to count as one item, even if they are packed and tagged separately.
Any of the items listed below may be checked in substitution of one piece of the free Checked Baggage allowance for each Passenger at no charge on a one-item-for-one-bag basis. If the item of sporting equipment exceeds 50 pounds in weight or 62 inches in size (outside length plus height plus width), excess weight and size charges may apply.
Maximum weight is 50 pounds and maximum size is 62 inches (length + width + height) per check piece of luggage. Effective for tickets purchased on or after December 15, 2012, for travel on or after February 13, 2013, overweight items from 51 to 100 pounds and oversized items in excess of 62 inches but not more than 80 inches will be accepted for an overweight and oversize baggage fee of $75 per item. For tickets for travel before February 13, 2013, or for tickets purchased prior to December 15, 2012, overweight and oversize baggage fee is $50 per item.
So if you had an oversized bag over 50 lbs and 62 inches. Then you will be charged.