That is another way of thinking about Whitworth v. Kling (8th Cir.), arising from a K-9 (named Dutch) biting a guest in his off-duty handler's house. The court rejected a Fourth Amendment unreasonable-seizure claim against the handler, because the bite was unintentional and not part of the officer's official efforts. The court treated the K-9 as the officer's weapon used to engage in force--in this case, the sort of unintentional force that does not violate the Fourth Amendment.
But note two paths not taken. One is to say that Dutch did not act under color because he did not pretend to perform his official duties----he was playing fetch in his yard off-duty, got distracted, and ignored commands to disengage--or use his position to enable his conduct. Of course, the text of § 1983 precludes that approach--"[e]very person" under color
Another is that the officer--off-duty, playing fetch in the yard, and not attempting or appearing to perform any job-adjacent acts through Dutch--did not act under color. Not sure why the court ignored that possibility or used the approach it did.
