From the video

Video: These Players Are About to Smash in Week 1
Brian Thomas Jr. is static. Brian Thomas Jr. is always playing the X on the outside. is not really going to be moved around to have schemed usage
Mentioned at 17:13 – 17:19Captured by STACKED 10 hr after posting

STACKED’s take

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Static X-receiver role limits schemed usage

Brian Thomas Jr. is described as a static X-receiver who plays on the outside and is not moved around the formation to create schemed mismatches.

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