If you want to play Swanigan at back up center, fine, I agree the options were limited.
But there is absolutely no way to excuse putting Swanigan in at PF.
The Mavericks lineup at the time was Doncic, Wright, Hardaway, Jackson, and Kleber. Who is Swanigan supposed to guard if Whiteside is already forced to the perimeter to guard Kleber?
The Blazers had already given up 31 points including SIX 3 pointers in the first 8:19 of the game. Again, why would putting Swanigan in WITH Whiteside be anyone's decision to slow their 3 point barrage down?
Swanigan comes in the game and not only does Stotts have him guarding a perimeter player but of all the possible options on the team he chooses Swanigan to double team Luka in a transparently weird way. The already hot Mavs hit wide open 3's on the first 3 possessions after Swanigan came into the game leading to scoring 45 points in the 1st quarter and 78 in the 1st half. Why would you send the slowest footed player on the roster to double Luka?
These aren't hindsight questions. I was at the game and asked these questions as they were happening to other people in my section.