I think this is just a coincidence. There's probably co-incident timings that cause his duck motion to happen at the same time as the punch.
>> Isn't one of the timing cues a camera flash? I forget for which boxer.
> Yup! a camera flash is for the first time you fight Bald Bull. The developer leaked that easter egg and said there was more, that's when I noticed this one.
Apparently there's a pattern of there being visual cues put in by the developers.
Original reddit post: https://www.reddit.com/r/gaming/comments/4dybvk/i_think_i_di...
It indeed looks deliberate.
I would suppose an easy test is to go the full round without attacking the boss and see if that spectator does the head nod at any point other than during the super punch.
http://arstechnica.com/gaming/2016/04/decades-later-a-new-mi...
The developers are quoted halfway down the page as having included the timing cues for opponents intentionally.
We (the gaming community) have known this since 2009 when that interview came out, so it's kind of amusing that people are making tech-based arguments trying to debunk a cultural fact they aren't familiar with. It could have been an unintentional artifact of the PRNG, sure, but it isn't. At the very least it was intentionally not removed.
If nothing else, those cues probably helped QA quite a bit.
When you look at how older video games are developed, you almost always have to first consider what the extreme constraints are. Nowadays you can get away with paying very little mind to, say, how much disk space a video game takes. Even optical disk space matters little, as additional content could be downloaded as a part of the game installation process.
On older games, however, disk space, processor usage, RAM, everything was in terribly short supply. As a result, lots and lots of shortcuts were taken. A more well-known example is how the Mario Bros clouds and bushes used the same sprite with a different color palette. [1]
So when developing a game under those constraints, the developer would have had to be keenly aware of how much was going on at any given time and whenever possible re-use any existing processes or assets. In Punch-Out there are several things happening on the screen at once, between the movements of the crowd and the enemy. When it came time to implement the "super punch", the developer would have probably wanted to re-use any existing RNG process already being run, rather than run a whole new RNG for that action alone, in the interest of conserving resources. In this case, they could have chosen the same RNG results that drive the head-bob in the crowd NPC.
[1] http://24.media.tumblr.com/tumblr_kz7gthD7UU1qbn1vmo1_500.pn...
That it happens when you need to throw a punch is not evidence of intent, as that is a pre-determined sequence. There are likely only so many sources of random-looking behavior available, so it's quite reasonable that a background character's movement would be tied to the same source as the source that determines how often the boss is vulnerable.
edit: To clarify, the two events are clearly linked, but that does not mean they were intended to be linked. I am in agreement with Zikes' reply.
But seeing as one of the game's creators has mentioned they liked to put in contextual cues for when things were about to happen, it also seems pretty plausible that it's intentional.
The subject of the interview suggests that there are lots of yet-undiscovered Easter eggs in the game.