When spectating, shift+(numbers 0-9) will switch to spectators in the relevant position (ordered like keyboard order). In teams matches 1-5 are mapped to team 1 players in race order (including respawns), and 0-6 are mapped to team 2 players so that 0 -> 1st, 9 -> 2nd, 8 -> 3rd, etc.

In settings you can disable the requirement to press shift and/or disable blocking key presses. If key presses are not blocked, they might activate game stuff if the numbers 0-9 are bound (via in-game settings).