Each player in NFL Blitz is rated in four categories:
 

While NFL Blitz's digital instruction manual doesn't mention what any of these attributes actually do, some rating descriptions appear on pre- and post-game load screens. EA Forum member, Yuri_B, has kindly transcribed all the ratings information into a handy list:

Speed 

• On OFFENSE & DEFENSE, speed modifies how quickly your Turbo Bar will drain and refill.

Power

• On OFFENSE, power helps your offensive line win their blocks, giving your QB more time to throw the ball.
• On OFFENSE, power increases the chances of breaking a tackle while carrying the ball. 
• On DEFENSE, power helps your defensive line win their blocks so they can get into the backfield with more frequency.
• On DEFENSE, power improves your chances of tackling a ball carrier in the middle of a special move, when you dive at them.
• On DEFENSE, power increases your chances of causing a receiver to bobble the ball when he is hit during a catch animation.
• On DEFENSE, power increases your chances of causing the ball carrier to fumble the ball when hit.

Skill

• On OFFENSE, skill reduces your chances of bobbling or fumbling the ball after being hit.
• On OFFENSE, skill slows down the kick meter, making it easier to kick field goals and punts.
• On OFFENSE, skill increases the chance that your CPU-controlled receivers will push down defenders immediately after the snap.
• On OFFENSE, skill improves your chances of beating a diving defender whenever you perform a special move. 
• On DEFENSE, skill increases the chances of your CPU-controlled players performing dives, pushes and interception attempts.

Recovery

• On OFFENSE, recovery allows your receivers to fake out defenders more easily while running their routes. 
• On DEFENSE, recovery makes your players more alert and reduces their chances of being faked out by a receiver's routes.
• On OFFENSE & DEFENSE, recovery gives players a better chance of not being tackled by doing a stumble animation instead of actually being tackled.