Grant Cohn: The specs on what 49ers want to see at NFL Scouting Combine

Don't merely watch the NFL Scouting Combine. Watch it how John Lynch and Kyle Shanahan will watch it.

When they're in Indianapolis next week, they'll search for specific players who play specific positions and have specific physical traits the 49ers desire. These are the positions and traits you should watch for, too.

POSITION No. 1: GUARD

Lynch and Shanahan have to find a starting guard, maybe two. That means they need to draft one during the first few rounds.

Last season, the Niners didn't draft any guards — they inherited Josh Garnett, a first-round pick in 2016. During training camp, Garnett hurt his knee and missed the entire season.

Garnett is big, tall and slow. Built to push defenders backward. He may not fit the 49ers' scheme. Shanahan likes smaller offensive lineman who run side to side. They don't have to push defenders backward. They have to be fast.

Based on his picks in the past, Shanahan will look for guards who stand between 6-foor-2 and 6-4, and weigh between 293 pounds and 305 pounds. 'Mini' guards. Then, he'll target ones who run a 5.15-second-or-faster 40-yard dash with a 1.75-second-or-faster 10-yard split.

Those are magic numbers for Shanahan.

POSITION No. 2: MIDDLE LINEBACKER

Before this offseason, Lynch and Shanahan probably figured they were set at middle linebacker. Figured they had Reuben Foster for the long haul.

Now, Foster is awaiting arraignment in two states for potentially four charges, three of which could be felonies. The Niners may not have Foster much this season. They have to find his replacement right now.

That may not be easy. The Niners want their middle linebackers no shorter than 6 feet and no lighter than 229 pounds. They also want them fast and agile. Have to run the 40-yard dash no slower than 4.6 seconds. Have to run the 3-cone drill no slower than 7 seconds.

Very few linebackers at the Combine will meet those requirements.

So, the Niners may draft two linebackers to replace Foster: a big, slow linebacker to defend the run on first down and second down, and a small, fast middle linebacker to cover tight ends and running backs on third down.

POSITION No. 3: LEO

That's what Lynch and Shanahan call their No. 1 edge rusher, their weak-side defensive end — the side away from the tight end.

Right now, their Leo is Cassius Marsh, who should really be a backup. Marsh has started only two games in his career and has recorded just six sacks.

The Niners like Marsh because he fits their physical profile for a Leo. Any Leo the Niners draft has to stand between 6-2 and 6-4, and weigh between 245 and 260 pounds. And he has to be fast and agile. The 49ers like speed rushers, not power rushers. A Leo has to run no slower than a 4.75-second 40-yard dash and a 7.15-second 3-cone drill.

Expect Lynch and Shanahan to draft a Leo who meets these requirements in the first two or three rounds.

POSITION No. 4: CORNERBACK

Of all the positions, the 49ers have the strictest physical requirements for cornerbacks.

They have to be no shorter than 6-foot, and their arms have to be at least 32 inches long so they can play bump-and-run coverage and jam receivers at the line of scrimmage. Any corners who don't meet those basic criteria, the 49ers won't even consider drafting.

And those aren't the only requirements: Corners have to be extremely fast (sub-4.5 in the 40-yard dash), quick (sub-7.0 in the 3-cone drill) and explosive (at least a 36-inch vertical leap). They have to be the most athletic players on the team.

Last year, the Niners drafted a corner who met all of these physical requirements — Ahkello Witherspoon. Now, they have to draft another one to pair with him.

POSITION No. 5: WIDE RECEIVER

Pierre Garcon will turn 32 in August, and is coming off a broken neck. Lynch and Shanahan probably will draft someone to sit on the bench for a year and replace Garcon if necessary in 2019.

Garcon is the starting flanker, or the possession receiver. He's the guy who makes tough catches over the middle.

Shanahan wants his flankers big — no shorter than 6-0, and no lighter than 210 pounds.

Shanahan doesn't care if his flankers are fast — they can run as slow as 4.55 in the 40-yard dash. But he wants them to be quick. Ideally, they'd run the 3-cone drill in seven seconds or fewer. And wants them able to jump high — at least 36 inches.

Think Jerry Rice.

POSITION No. 6: RUNNING BACK

If Carlos Hyde signs with another team, the 49ers probably will draft a running back in the first few rounds. And any running back the Niners draft before Round 6 will meet two requirements: He'll be agile, and he'll be one of the fastest players at the Combine.

His height won't matter, and neither will his weight. Lynch and Shanahan are looking for running backs who will run faster than 4.45 in the 40-yard dash, and faster than seven seconds in the three-cone drill. That's all.

The past three running backs Shanahan drafted all met these requirements. He drafted Joe Williams in 2017, Tevin Coleman in 2015 and Chris Thompson in 2013.

If Lynch and Shanahan wait until after the fifth round to draft a running back, then they will eliminate their speed requirement and take anyone who runs a good time in the 3-cone drill. That's what Shanahan did in 2012 when he was with the Washington Redskins. He used a sixth-round pick on Alfred Morris, who was slow but nimble for a big guy.

BONUS POSITION: QUARTERBACK

You may think the Niners are set at quarterback. They're not.

Their starter, Jimmy Garoppolo, has started only seven games in the NFL. And their backup, C.J. Beathard, has started only five. And he lost four. And his quarterback rating was 69.2.

While Garoppolo showed promise, Beathard did not. He showed nothing. He merely survived. Avoided serious injury. Didn't earn a spot on the next season's team.

The Niners have to draft another quarterback in case Beathard or Garoppolo or both fail in the near future, or get hurt.

Shanahan typically drafts medium-sized quarterbacks — between 6-2 and 6-4, and between 215 and 225 pounds. And they're usually mobile. They run the 40-yard dash in faster than 5 seconds, and the 3-cone drill in faster than 7.1 seconds.

In addition to the physical attributes, Shanahan wants quarterbacks who graduated college and had some experience running a pro-style offense.

Shanahan may or may not find his type of quarterback at the Combine this year. But, he'll look. You bet he'll look.

Grant Cohn covers the 49ers for The Santa Rosa Press Democrat and Pressdemocrat.com. You can reach him at grantcohn@gmail.com.