Stopping No. 7 will be a challenge for the Buffalo Bills' defense against the San Diego Chargers on Sunday.
But stopping No. 21 might be three times as important to the Bills' defensive success.
Rookie running back LaDainian Tomlinson has been the biggest key to the Chargers' offense this season.
San Diego's No. 21 ranks fourth in the NFL in rushing with 544 yards in six games. And he's the foundation of the ball-control attack Chargers offensive coordinator Norv Turner loves. The Chargers lead the NFL in time of possession, controlling the ball an average of 32 minutes, 34 seconds.
"If I'm them, I'm running Tomlinson over and over until the defensive line stops him," Bills defensive end Phil Hansen admitted.
No doubt this thought has occurred to both Turner and No. 7, Chargers quarterback Doug Flutie.
The Bills are tied for 27th in the NFL in rushing yards allowed at 138 yards a game. They are next to last in average gain allowed, at 4.2 yards a rush.
The Bills' defense has allowed 100-yard rushers in three of five games. Indianapolis' Edgerrin James gained 111. Pittsburgh's Jerome Bettis gained 114. The New York Jets' Curtis Martin gained 135.
"He definitely presents a challenge," Hansen said. "There's no sense in Flutie having to pass if they can run Tomlinson hard all day."
"He's been a huge factor in all their wins," Bills linebacker Keith Newman said. "He's been the man for them."
Tomlinson, the Texas Christian University product, was the fifth pick in April's draft. A 5-foot-10, 221-pounder, he is the fastest back the Bills have faced and probably has the quickest cutting ability.
"He's got great vision, and he does a good job on yards after contact," Bills coach Gregg Williams said. "We've seen some times where he can be stopped at the point of attack, but he can turn a bad play into a good play by going out the back end. It's a lot of the same things you saw Thurman (Thomas) do here for years."
The Bills' defenders are emphasizing the need to stay in their lanes to contain Tomlinson's cutbacks.
"He's a cutback runner and picks his holes good, so we have to stay in our gaps," defensive tackle Pat Williams said. "I just have to tell my 'backers, "I've got my gap, you stay on the backside.' That's one thing we've had to work at. The 'backers are young, so I don't always know what they're doing. It was different with Sam (Cowart). I'd know where Sam was going to be all the time. But we're getting better at it."
The season-ending injury to Cowart likely eliminated any chance the Bills have at being a dominating run defense this year. There's simply no way to replace the Pro Bowler.
But the Bills like what they have seen from rookie fourth-round draft pick Brandon Spoon, who has taken over Cowart's middle linebacker spot.
The Bills' run defense was improved last week against Jacksonville. It held the Jaguars' Stacey Mack to 85 yards on 15 carries. The good news was Mack managed just 28 yards on 13 of his carries. The bad news was he got 29 and 28 on two others. A speedier back might have taken one of those all the way for a touchdown.
"I think we played better," Spoon said. "We had a couple technique and assignment busts on those long runs. But we did a better job. We need to keep improving. I think we're starting to jell a little and get used to each other's tendencies."
"I see us doing each week better in that respect," Williams said. "You'll see one or two or three runs in a ballgame be the most significant part of those yards being piled up.
"The big thing is you can't let a bad play affect you the next three or four plays in a row. That was one of the things that I thought defensively we didn't do a very good job of last week. In the third quarter when they did have one run, the next three or four plays were, "Poor ole me.' You can't do those things. We've got to live for another down and get focused on the next snap."
After gaining more than 100 yards in three of the first four games, Tomlinson was held to 74 and 58 yards the past two weeks.
That could mean defenses are getting a handle on the Chargers' run game. Or it could mean he's due for a huge day against the Bills.