Should the Senior Bowl or the Combine Workouts Matter?

[Sheriff Gonna Getcha]

I love to watch the Senior Bowl and the combine workouts, but do they really matter? Each year players watch their draft stocks rise and fall based on the Wonderlic, 40-times, etc. Take, for example, Terrell Suggs. Terrell Suggs was thought to be a top five selection in the 2003 draft, but slid down to the Ravens because of slow 40 times in pre-draft workouts. Vince Young's draft stock might have slipped a few spots due to his Wonderlic score (a wildly inaccurate predictor of football acumen). Players are now so polished up before player interviews at the Combine that I don't think that 10 minute player interviews can be that meaningful.

In my mind, the Senior Bowl is almost totally worthless as a scouting tool since it provides such a small "sample" and is a game involving very basic schemes, new coaches, and new teammates. The combine seems almost as useless. I would think that, save the medical examination portion of the combine, it too has minimal value.

Obviously I am not a scout, so would someone please explain how they are useful and why a player's draft stock can ascend or plummet so rapidly?