Значит, что между теми списка, "judges" являются - как сказать?- самом непохожи на других. I hadn't really considered before how idiomatic "odd one out" is. So, that is, judges fit into the category (of sports 'officials') slightly less well than the other three.

Dominic, what does this mean? Judges are the odd ones out. Lots of good luck to you!

Linesmen are usually used in field games where there are several 'officials'. Football and hockey, for example. Linesmen enforce rules of position generally - 'offside' calls etc. Umpires and referees are fundamentally the same, and the title depends only on the tradition of the sport - although, for some reason, generally umpires (in sports with them, such as tennis or cricket) don't tend to move as much as referees. Judges are the odd ones out. Judges aren't generally involved in rules, but in scores.