Well, here's my line of thought, you'd have a preset list of events, something like:
1 = connect,
2 = kill,
3 = suicide,
4 = global login,
5 = respawn,
...
Then the first field would be the client id (on the server), so you might have something like:
2|1|12.34.56.78|JoeBlow|20 (JoeBlow connected)
2|4|56789 (JoeBlow logged in)
2|5 (JoeBlow respawned)
1|2|2|1 (Some other player eliminated JoeBlow with a trracer (weapon id 1))