I am not at all familiar with coins of Pertinax. However, he seems to have a rather distinct beard which I believe I see here: It's only 19mm, so much too small to be an As. I can't read any of the legend, except perhaps a "C" on the left. The reverse is entirely obliterated.
My first guess would be a Provincial of Septimius Severus. The beard does not strike me as like Pertinax. In this condition, ID is unlikely.
Ah, that is much more likely than a Pertinax. I'm used to the distinctive beard on the imperial coins of 7Sev, but I suppose I was too wishful in my thinking.