I hate the 4-2-5 on passing downs. It places a huge need on the rarest players in football. IE DTs who are good against the pass. There are really only a handful of guys in the entire NFL that fit that category. Dockett is one such guy, the issue is that Williams isn't. If he was he'd be a probowl level player and he's just not.
There's a reason that the best Defenses are going more to a 2-4-5 on passing downs.
Steelers go with two Antonio Smith/Ziggy Hood/Brett Kesel based on health. They then move up one or both of Harrison and Woodley to give the look of a 3/4 man front.
Packers go with Cullen Jenkins and BJ Raji, while moving up Clay Matthews.
If by 4-2-5 Horton means that Campbell and Dockett will be playing in the middle and he will walk up Schofield and the new OLB than that's fine and great. If he means that Dan williams is in on passing downs, that's not so great.
Regardless I think that Houston fits that role better than anybody. He's had experience with his hand down and playing upright and was excellent at both. He's not undersized and is stout against the run.
Campbell-Williams-Dockett
Schofield-X-Washington-Houston
I think is good enough against the run. Especially if the X is replaced with Nick Barnett, and not somebody undersized.
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Schofield-Campbell-Dockett-Houston
Barnett-Washington
Looks okay to me on blatantly obvious passing downs.
The 2-4-5 is nothing more than a variant of the 4-2-5 where 2 LBers play up on the line from a 2 point stance. It's the same personnel with the same responsibilities and most teams, Pittsburgh included, refer to it as a 4-2-5 regardless if there are only 2 down linemen. Most teams will vary whether the OLBs put their hand in the ground or not in an attempt to disguise their intent.
It requires 2 quick penetrating DT's who generally shoot the B Gaps to provide pocket contain, 4 linebackers...3 of which generally drop into intermediate coverage while the fourth generally rushes and 5 DB's to cover. There are varying calls that can send 2 LBs, a LB and a DB or any other combination of rushers.
As for our personnel, our down linemen would probably consist of Dockett and Campbell, both of whom are able to penetrate on a pretty consistent basis. Couple that with Campbell's tall frame and his long arms, he's been pretty good and knocking passes down quite regularly. Dan Williams wouldn't be on the field just as Pittsburgh pulls Hampton.
Our Lbs, just as in our 3-4, will need to be upgraded. Washington would be inside and hopefully an upgrade at the other inside position. O'brien Schofield who is looking to get back up closer to 250lbs would probably be one on the outside and hopefully someone such as Robert Quinn though I think Haggans would get the nod over a rookie.
We need to get bigger and more athletic on defense and start weening away from our older guys who have lost a step. Our LBs have plenty of experience, but they just can't keep up with half the league anymore. We'll have a hard time stopping anyone out of any formation if we don't drastically improve our LB corps.