What constitutes a boot bag when checking in with skis? My dad flew DL yesterday from DEN-ATL-PVD. He had his boots placed in a little rolling suitcase (and ONLY his boots, there was nothing else in the suitcase) with his skis in a separate ski bag. The gate agent (and her supervisor) refused to accept the rolling suitcase with the boots in it as a boot bag & wanted to charge for two pieces of checked luggage. They kept insisting that a boot bag must be the type of bag that one would purchase at a ski shop. Neither would budge on their position & only finally did the supervisor tell him to take the rolly suitcase, a small carry-on, AND a reusable grocery bag all as carryons. However, Delta's website does not define what constitutes a boot bag (it only says the combined weight of both pieces must be under 50 lbs & that the linear dimension limitations are waived). I was with my father when he checked in & having read the requirements beforehand, I thought their interpretation was irrational. The linear dimensions of a small rolly suitcase are not that different than a boot bag one would buy in a ski shop (which often can fit more than JUST boots). Moreover, he has done both on other airlines & also on his outbound DL trip to DEN, so their insistence seemed doubly arbitrary. Furthermore, why should someone have to purchase a specialized bag when one we already have a piece of luggage that works perfectly fine for the purpose of carrying boots (it didn't seem terribly green on Delta's part!). I have copied the information from DL's website below.

Ski or snowboard equipment Ski and snowboard equipment are accepted as checked baggage.

An item of ski or snowboard equipment is defined as:
One ski/pole bag or one snowboard bag, and One boot bag
The combined weight of the ski/snowboard bag and the boot bag may not exceed 50 pounds or excess baggage fees will apply. The outside linear dimensions may exceed 80 inches and no excess baggage fees will apply.

Any advice FTers? It would be much appreciated.

Last, if this is in the wrong forum, please feel free to repost. (My friend advised me to post it in the DL forum, rather than TravelBuzz where I had initially posted it). While our experience happened on Delta, it is a larger Q because we would like to know for future trips. Thanks!