I suspect he lost the job when he entered the portal- not before. If the coaches really did firmly decide on Sisson as their man leaving Grainger with no choice but to accept a better offer, then that’s on them. But I really doubt that’s what happened.
It's all speculation at this point. In his public comments, Grainger was complementary of the Furman coaches and staff.
Again, I realize that the backup QB is always the "most popular" guy on the team, but if you just look at the numbers, it is not as though Grainger had a vice grip on the job.
Arguably, Grainger in 2019 was the worst passing output of any Furman QB over the last 20 years. The only comparable season may have been Dakota Derrick/Cody Worley in 2010 (we were 5-6 that year).