Asking for a friend. Imagine the whole trap is installed (it was removed for a new vanity). Would you then consider this an s trap? Again, imagine the actual trap is screwed unto the outlet connector you see here…
In my opinion, no, I would not consider that an s trap. That little drop before it goes horizontal is not going to siphon the trap.
I can’t tell. If it drops back down vertical, then it’s starting to look more like an s trap.
Larry,
Im with you on this one…interesting how opinions vary. In this case the gc says its fine and the inspector says not so fast. I told him to defer toba licensed plumner as our job is to observe and report. We see something that looks off, we call it out and call in the experts…
Forgive my typos, fat thumbs…
The GC is fighting the wrong fight, IMHO.
It is an easy fix.
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The answer to your question partly relies on what we can’t see behind the wall. Is the drain vented back there?
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Yup, and we just found the local code that says the trap arm has to be twice the lenght of the diameter of the pipe. Just cautioned the inspector that we are not code inspectors and to deder to the AHJ.
Ty for the replies!!
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Ryan, the horizontal run is basically non existant, so therefore its an s trap…that seems to be the consensus with the local code as well now that we found it…
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Some of them will spin the tallest tales to save themselves 5 seconds or 5 cents. 
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An S trap goes into the floor, a P trap goes into the wall. I don’t nitpick the rest. I grew up with clawfoot tub and S trap sinks, no sewer gasses. So the big question is does the sink drain properly. Can’t answer that yet.
I appreciate these perspectives. There might be a plumbing “gotcha” moment here, but an actual defect or performance issue is inconclusive, in my opinion.
I would likely write it up as a concern since it missing the horizontal tailpiece, I could not operate the drain, and the vent is not visible.
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Respectfully agree and disagree. I grew up with aluminum wiring and asbestos…codes change and evolve. S traps were the bomb back in the day and then everyone realized that they get syphoned out, so codes changes. Is it gonna burn the house down, no. Is it gonna let sewer gasses back in the house, prolly not, but maybeee… so im with you and not at thebsame time 
Like many inspectors, I always ask the buyers if they have any specific concerns about the home. On an inspection about ten years ago, I asked this to an elderly couple. She immediately said that checking for S-traps was of the utmost importance. The house that they had been living in had them. They had lived in the home for years and never had a problem. That was until the last couple of years of living there. She kept on getting sick and to the point where she was spending extended stays in the hospital. It got bad enough that the police got involved and investigated the husband for poisoning her. During the investigation, they determined that it was from sewer gas and cleared him. For whatever reason, it did not affect the husband at all.
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When a P trap is installed it would likely be a S trap, although the plumbing might be done properly when the new vanity & sink are installed.