This is a BNSF stack train at the Port of Tacoma, delivering a train to Tacoma Rail. As part of normal operations, this train comes west across Stevens Pass, through Seattle and down (south) to Tacoma. At this point the head end power is on the wrong end to take the train through the BNSF Tacoma Yard, over the Puyallup river and to the Port of Tacoma and Tacoma Rail. So, they typically run around the train and drag what was the rear end of the train to Tacoma Rail. The trains are often built so that the lighter cars (single stacks) are on the rear, as was this train.
The procedure at Tacoma Rail, is to run through main yard and as far up along Port of Tacoma Road, as is required to clear the track they will shove into. This train was long enough that it made the curve across Port of Tacoma Rd and then west along Lincoln Ave. Once clear of the setout track, they reversed directions and shoved (on the lighter cars ) and into the setout track.
As I understand it, in this case to add to the problems, the rear end brakes may not have been fully released. Shoving the lighter cars against the heavier cars, with maybe brakes not fully released and on this curve, resulted in the middle car of the 3 pack, picking the turnout (not visible to the right) for the stub track (lower left) while the rest of the train's momentum pulled it toward the curve. Eventually and after pulling the turnout at the center, toward the curve by about 2', something had to give. The cars popped off their trucks, the center car took out a power pole and re-landscaped the area between the tracks, before the crew realized the problem and stopped the train. This is the 3rd time at this location in about a year, that a BNSF crew has done this and likely the last, as there will be (or already has been) operational changes.