On thing that no one has mentioned is that Federal Marshalls are often really big guys.

I once received a traffic ticket, unfairly, I thought, so I checked the "I plead not guilty and request a trial" box.

A couple months later, after I had forgotten the whole thing, slightly after dark, I pulled into my long, country driveway, only to find myself bathed in searchlights and being addressed through a bullhorn. I had not read my ticket carefully, and neglected to remit bond equal to the the fine(about $50, at the time), and was under arrest.

Two very large individuals approached, and explained why I had been singled out for the extremely cinematic honors. They explained that there was a new court, especially set up for minor traffic infractions, with a new judge, who had hoped for a much more important appointment.

They were friendly guys, and we had them in for coffee, and chatted about the business of Marshalling. As Joe alludes to above, it involves giving things to people who don't really want them, and often requires taking them places that they don't really want to go. Size, it develops, is an advantage in these situations.