Coach requests help mechanic

[dcvh]

High school game..4th inning 2 outs R1 on third..I'm in C position..ground ball to deep short..long throw- big stretch by 1st..throw beats runner by 1/2 step I bang out runner but have no clue if foot was pulled..infield starts off field.. R1 has peeled off toward his 3rd base dugout without touching home plate...coach requests I get help on pulled foot..PU tells me foot was pulled..I call runner safe..
Questions...what do we do with R1..award him home, return him to 3rd or bang him out for abandoning his base..One can easily see a myriad of potential issues..bottom 7th tying or winning run..other runners on base
We returned R1 to 3rd but heard, shall I say, vigorous arguments from both coaches for awarding home and for banging R1 out for abandoning base.
Both of these arguments have some merit...what is proper procedure?