It's the knock-kneed-ness (say that five times, fast!) more than just how wide their legs are set. I doubt I'd be bothered enough to write them off and look for alternatives at this point if they were the only cockerels I had but it's something to consider when comparing them to other options. And I do plan to selectively cull over future generations in favour of heavy, fast growing birds on the meatier end of "dual purpose" - nothing as extreme as commercial broilers, but being able to comfortably support their own weight and move around is still a concern when the keepers will be living full lives and not just the few months it takes to get them up to slaughter weight.
Not that breeding show winning birds is a goal for me, but I've been reading
@speckledhen's Omega Rocks thread and she mentions stance as being something to look for
e.g. here and a couple of posts later (speckledhen - no obligation to read any of this or reply, just tagging you because it feels rude to mention someone 'behind their back' as it were)
It's really hard to judge when they're standing naturally and when they're just in an odd position though - I took these today, just moments apart.
A (couldn't get a shot of him today where it was as pronounced as it sometimes is):
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B:
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And the two older barnyard mix cockerels for comparison. They're both standing much more upright than the Rocks are in their photos but when these two lean over to peck at the ground, their hocks bend in more of a straight backwards direction rather than inwards.
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Speaking of the older boys, they both went off to roost tonight while "their" pullet was still busy chickening around the far end of the plot. (The Sussex pullets have started sharing their coop at night now but still prefer to be with the others during the day.) She knows the way back but it was getting dark by the time she realised they'd gone and I had to guide her back myself. I don't expect perfect flock leader behaviour at their age, without an older cock to learn from, but not being even the slightest bit bothered about her being missing is a mark against them.