Good topic.
Top 5 leading contenders, although this is admittedly pretty hard to do with a team like the Hawks.
And just because I seemingly have to make these types of caveats here, I'm not saying ANY of these guys WILL have a down year, I'm just talking through who the contenders are (and why their contenders) if someone DOES have a down year.
1) Cliff Avril: I don't think he'll have a *down* year, but he'll probably have a more typical year for himself than last year, which might get talked about as a "down year" even though it isn't (last year was just an "up year" for him). He's also 31, and although age shouldn't be a problem yet for him, I guess it's worth mentioning if we're making small differences.
2) Frank Clark: He's one of only two high performing guys on the Hawks who hasn't strung multiple good years together yet (the other one comes next), so if you have to pick somebody the guy who hasn't shown it year in and year out yet isn't a bad pick. He's #2 and not #3 because so far in his young career he's a pass rush specialist whose signature stat is sacks, and those can really fluctuate from year to year. He could basically be the exact same guy from last year and end up with 6 sacks instead of 10: it's what happens with a stat like sacks in which the difference between 6 and 10 is the difference between getting a sack on 1% of plays versus 1.4% percent of plays -- a few banana peels across a season one way or the other and you're thought of as an entirely different player.)
3) Justin Britt: No reason really except that after Clark he's the only other good player on the Hawks who hasn't strung multiple good years together yet, so once again, if you have to pick somebody the guy who hasn't shown it year in and year out yet isn't a bad pick.
4) Richard Sherman: Was he injured last year, or is his lateral agility starting to decline? Lateral agility is usually the first to go, it was never a strength of his, and for CBs in particular when it goes it goes hard and fast. 29 is still a little young for that, so I'm going to go with injuries last year as the culprit, but in a hard to make list like this that it could be an age-related decline in lateral agility gets him to #4. You also have to factor in that although the chances of it happening are slim to none, he's the most likely player on the Hawks to have his game suffer from emotional implosion.
5) Michael Bennett: Whispers of him declining last year were overrated. He was just coming off of a statistical "up year" and missed a third of the season due to injury. He's only here because he'll be 32 and there's nobody else to go here.
DIDN'T QUITE MAKE THE LIST: Prosise, Lockett, Joeckel: Nothing wrong with any of them, but overheated expectations can cause replications of what they've done in the past to lead to accusations of "down" years.