Before we compare the two, let's first take a look at what Brown does that allows him to succeed where Richardson cannot. On this play, the Colts have a 1st and 10 at their own 46-yard-line. The play is designed to go over right guard, with two tight ends to the right of the formation. Here's what it looks like at the snap.
Brown sets up his blocks, allowing Gosder Cherilus and Mike McGlynn to get to where they need to be. Still, when he first makes his attack, there does not appear to be much room for him to break through. He finds the tiny bit of space between his lineman, breaks one arm tackle, and busts a 15-yard run. It's plays like this that the Colts have not gotten from Richardson since making the blockbuster trade. See, just look at how tiny that hole is when Brown makes his move.
Now let's put the two of them side by side. The following are two very similar plays, designed to hit the same holes. They both take place on first down with 10 yards to go in the first quarter. Here is the formation with Richardson in the backfield.
Here's a look at the formation with Brown in the backfield.
On both plays, the Indianapolis line opens a hole over left guard. The only difference is the runner in the backfield. Richardson dances a bit before getting to the hole. By time he gets there, cornerback Alterraun Verner shakes his blocker and is in position to make the tackle. You can see just how open the hole is in the screenshot below. The fact that this play only goes for one yard is on Richardson.
Brown, on the other hand, wastes no time getting to and through the hole. As we can see in the below screenshot, that urgency gives him time to break one tackle and pick up nine yards.
Finally, let's compare a toss play that Brown converted into a six-yard touchdown run while Richardson managed to pick up just four yards on one of his most indecisive runs of the night. Again, the look of the formation at the snap, with Richardson.
And here it is with Brown.
Richardson appears to have his blocks set up well here. In fact, it looks as though he has two options. The play is designed to go inside, but he might actually be able to freelance a bit and take it to the sideline for a big gain. He could stick with the original design, as well, and pick up a solid chunk of yardage by hitting the hole right in front of him. Here's the point when he needs to make a decision.
Instead, he simply follows directly behind his blockers, runs into a wall that should have been serving as a convoy, and slips and falls on his own.
Brown ran the exact same play properly earlier in the game. At the point in the first screenshot below, Brown has just caught the pitch from Andrew Luck. He has already put his foot in the ground and has begun making his cut up field behind Samson Satele. In the second screenshot, you see the fruits of that decisiveness. Brown has a monster hole that allows him to scoot right on into the end zone.
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