I don't disagree that Eammon Walker could have been a better actor in the Concussion role, but studios will sacrifice quality for money 10 times out of 10, and Will Smith still moves the needle for enough people out there (myself not included).
I haven't seen the first movie, so I'm assuming there was at least one exchange of dialogue between... Lee Marvin and Jim Brown in The Dirty Dozen Jim Brown and Al Pacino in Any Given Sunday Al Pacino and Robert DeNiro in Heat.
