At the Olympics in Athens 2004 the typeface Gill Sans was used for many promotional materials: on billboards, in the swimming pool, and also on shirts. Shirt numbers in this typeface look very clear and bright. The only problem with Gill Sans is de figure 1. Because it just consists of one vertical stroke, it can be mistaken for a lowercase l or a capital I. Moreover, all figures have the same width, which means that the figure 1 stands alone in a lot of white space.
Sadly enough this good example isn't followed by the organisation of the Olympic winter games in Torino 2006. Shirt numbers in this event are set in Arial.
Figures from Gill Sans
Figures from Arial