I have one that came to me with similar marks, almost like someone played hockey in it. (gasp!) Scrubbing with pretreater and oxyclean didn't touch it. I gave up, since it's not a white jersey and really isn't very noticeable. I would probably try goof-off next. If it looks oily, maybe mineral spirits? I've never had to try that, though, and would definitely test an airknit swatch first for staining.