Some background information for context, this is an 8u machine pitch game, the base coach is really the pitching machine operator and head coach is at 3rd. Immediately after the play ends the machine operator chirps to head coach "we got a problem, outfielder can't come into the infield and tag a runner." Head coach looks at him and then at me and says with eyebrows raised "obstruction!" I immediately say no, gave him a quick explanation of what is in the rules, and that fielder is the word used in defensive scenarios within the book, fielder once again can be anybody, and a tag can be made by any fielder according the the term definitions within the book. Base coach then comes over and says "I've known baseball all my life and this has never been legal, T-ball, 8u, 10u, an outfielder can't make a tag." Also in the stands is the parks commissioners wife who sides with coaches and claims in the one in the wrong.
I did some digging between innings and found a little bit of evidence that supported my explanation.
Also said base coach gave me a hard time earlier in that teams season when they sent a runner from third to try and score who ended up being beat by a mile by the throw from F3 and eventually being tagged out in a pickle wanted an "interference" call because the catcher stood on the first base side of the plate while the runner was maybe 10 feet past 3rd in the initial throw from F3.