Ideally players should give 100% effort every game, but that simply isn't true.
Heck the only reason we are even discussing the possibility of an upset is because the Ravens rarely give 100% against inferior opponents. I'm sure the Chiefs will come out fired up and ready to play, but as soon as Cassel turns the ball over some of their players will lighten up.
I watched every Rams game last season and believe me plenty of players gave up once they got behind. Which is probably the reason 50+% of that team isn't in the league anymore.
That's simply not true. They may play like crap against some inferior teams but I would never accuse them of not giving 100%. The results might not bear out maximum effort but that's not for lacking of trying.