Based on a conversation I had with nero outside of the forums, this is how I understand it:
The offensive scouting shows the number of times your opponent has run a certain play this season and the average yardage result.
The defensive scouting show the number of time your opponent has run a certain play this season and the average yards the team they were playing at the time garnered against that play.
By "checking" a play, you are "preparing" for that play in practice. What that does is raise your teams "familiarity" with it, so that your players are more likely to recognize that play when you are playing your opponent, therefore hopefully taking the right action on offense/defense to most take advantage of the play called by your opponent.
