You could also look here:
http://www.terrybrownenglishmartialarts.com/
the key is that during the early medieval period the warrior elite class would have been trained, from a young age, in martial arts. As (we currently believe) that Druids typically came from the warrior elite class some could well have been 'quite handy' when it came to a fight.
There is also :
The English Warrior from earliest times to 1066 - Stephen Pollington
available from - http://www.asbooks.co.uk/. I don't think there would have been much difference between the Fianna style warbands and the Beowulf style warbands at that time.


