JJ's contract is 3 years, $33.75M. The Browns already paid him a $12M signing bonus so if the Rams traded for him they'd have him the rest of this year plus the next 2 seasons for $21.75M. (An average of $8.7M a year if you figure he'd be a Ram for 2 1/2 seasons. For comparison purposes, there are 17 safeties in the league averaging more than $8.7M a year.)
JJ's salary for this year is $1.25M. The Browns have already paid him 7 of his 18 paychecks: the Rams would be on the hook for the remaining 11. That comes to $763,889.
And that would be the cap hit for the Rams in 2021: $763,889.
In 2022 the cap hit would be $5.35M
And in 2023 it would be $11.1M
Finally, in 2024 - the first of 3 void years in JJ's contract - the Rams would take on a $4.05M cap hit (even though JJ would not be playing for the Rams.)
Contract details from [
overthecap.com]
AlbaNY_Ram