Listed at 5'9" 216 lbs., Stacy is a squat, powerful back in the mold of Trent Richardson, but with less publicity, at least thus far into their careers. Unlike Richardson, Stacy has been able to find space and cutback lanes in 2013. A more apt comp at RB may be Frank Gore, listed at 5'9" 215 lbs, a physical cutback runner that lacks pure breakaway speed, but maximizes yardage with great vision and patience carrying the ball. Stacy benefits from sound blocking provided by his O-line, but he is also able make plays when the blocking is imperfect, a trait that separates the good running backs in the NFL from replacement level backs.
Sam Bradford hit injured reserve after getting hurt @CAR in week 7 and the following Monday night, St. Louis hosted the Seahawks. Despite being the focal point of one of the better NFL defenses, Stacy's talent was on display and he put up his biggest rushing total of the year including six rushes of 10+ yards. Let's take a look and see what Stacy is doing with his opportunities.
1st&10 in 1Q vs. SEA
St. Louis is going to run a counter to the left (our right), where the STL OL will block to the right, trying to get the SEA defense to flow with them and provide open space for Stacy when he gets the ball going in the opposite direction. TE Lance Kendricks (#88) is going act as the lead blocker on this play, coming across the formation to block DE Chris Clemons (#91). Clemons does a good job of crashing down on the running lane and beating Kendricks' block, but Stacy has already made his cut back inside behind DT McDaniel (#99) and picks up a chunk of yards before running into Earl Thomas.
1st&5 2Q vs. SEA
Another counter run to the left, but this time run from an Offset I-formation with the FB Cory Harkey (#46) as lead blocker. Clemons (#91) again crashes down inside, but this time MLB K.J. Wright (#50) attacks the backfield off Clemons' outside hip and is in position to stop Stacy at the line of scrimmage. Stacy instinctively reads Wright and quickly plants his outside foot and cuts up field, using his strength to power through Wright's arm tackle and pick up 10+ yards after initial contact.
2nd&2 in 4Q vs. SEA
STL is trying to run a simple dive out of an I-formation between the RG and RT. SEA is set to stop the run on 2nd and short with safety Kam Chancellor (#31) lined up next to the MLBs. The two MLBs and Chancellor all read the run and flow to their left to plug the gap, but Stacy sees the space develop on his left and immediately cuts back to the open space. Stacy busts out a small stutter-step to get by Browner (#39) before breaking Thomas' tackle and nearly picks up 20 yards.
2nd&10 2Q vs. SEA

The Rams are trying to run right up the A-gap, but DT Brandon Mebane (#92) is going to shoot the gap and take C Scott Wells (#63) into the backfield. Stacy immediately hits the brakes and makes a jump-cut to avoid Mebane and loses all his forward momentum. Stacy quickly kicks it back into gear and accelerates into open space. The extra time it took for Stacy to get to the line of scrimmage enabled Stacy's Ram teammates to clear the Seahawks out from the middle of the field freeing Stacy to rumble untouched for 9 yards before being contacted.
1st&10 1Q vs. CHI
This play comes against the more banged up and less formidable Bears defense, but it is a good example of Stacy's bread and butter cutback ability. The Rams block to the right (our left) at the snap, drawing the MLBs in that direction. Shea McClellin (#99) crashes inside on the right and Stacy breaks his run outside as soon as the FB picks up McClellin and he is off to the races. Stacy draws Chris Conte into a bad angle with a little hip shimmy and picks up another 20 yards before he is run down.
Zac Stacy was a 5th round draft pick in 2013 from Vanderbilt with an average if not respectable Speed Score of 100.8, but once he got on the field he has impressed with an ability to find cutback lanes. Stacy's combination of power, speed and vision makes him a prototypical "work horse" type of back that can wear down and punish defenders over the course of a game. The Rams QB for 2014 is still very much up in the air at this moment, especially since St. Louis holds Washington's first pick as well as their own, but whoever ends up taking snaps next season, he will benefit from Stacy's contributions running the ball.
I was going to post this last week as a preview of what the 49ers stout run defense was going to be facing in Week 13, but Thanksgiving interfered, so I figured I could turn one post on Zac Stacy into two posts. Part I talking about how good Stacy has been and Part II about how the 49ers were able to stifle him in Week 13. So stay tuned for Part II, coming soon.