I think Robbie is therefore proposing something new, based on a supposition that there are differences among pitchers in how they give up HRs. Jack Morris was supposed to be good at pitching-to-the-score, for instance. Except, as I recall it, when someone actually dug into his results game by game, they couldn't actually detect any such pattern. I'd need to see some evidence that some pitchers are more prone to situational HRs than others, before investing much time in constructing a new stat. My guess is that pretty much every pitcher gives up more HR with the bases empty, because they all pitch differently when men are on base - and if some pitcher happens to have results that vary from this pattern in a given season, it probably is just Small Sample Size (only a dozen or two HR in a season, after all) and the pattern doesn't carry over to the next season.