Goodman didn't want to play Fred Flintstone, so Spielberg announcing his casting choice in a somewhat public meeting put him on the spot and made it hard/impossible to refuse:
to coerce or intimidate, as by threats
to sandbag someone is to trick or bully them ...
John Goodman still starred in Always: he played Al Yackey, the best friend of protagonist Pete Sandich. Here he is on the poster:
The Flintstones didn't begin filming until 1993, four years after Always was released, so Spielberg could cast him in the former without affecting his participation in the latter.
As for why Goodman felt sandbagged, he may have ...
From The New York Times
So why was Swinton playing Lutz Ebersdorf?
“Undeniably, I would have to say, for the sheer sake of fun above all,” Swinton emailed. “As my grandmother would have it — a motto to live and die by — ‘Dull Not To.’”
Still, Swinton and her director had more in mind than just playfulness. Guadagnino had always conceived “...