So as a case study, we'll look at Anglo-Saxon England in the decade from 870-880, at the culmination of the Viking 'Great Army''s activity in England. 'Defender' is a slightly muddy term, as Anglo-Saxon tactics called for an aggressive defence, marching against attackers wherever possible, but broadly speaking England was on the defensive.

In the 11 years 870-880 (inclusive), The Anglo-Saxon Chronicle records 19 battles between elements of 'The Great Army' and defenders from various English kingdoms, principally Wessex, but also Mercia, East Anglia and Northumbria. Of these 19 battles, 6 are recorded as English victories, 4 as Viking victories, and 9 are left unrecorded as 'general engagements' fought in 871 specifically. In these cases, the ASC does mention that nine Danish earls and one king were killed in the year overall, more than the names listed of those killed in the major Wessex victory at Ashdown, which suggest that many or all of these smaller engagements were English victories, potentially defensive actions against small-scale raiding or scouting forces.

What constitutes a victory, and how meaningful it is, can be hard to discern. In some cases, the English inflict great casualties on the Vikings but are forced to withdraw, leaving the Vikings in possession of the field. At Wilton in 871, for example, a small English force manages to stand against the entire Great Army and actually rout them, until the Vikings realise just how few English there are and force them to withdraw before they're surrounded.

Asser mentions that English defences are spread incredibly thin by hundreds of small scale raids and skirmishes which sap English manpower, but are too minor to be worth mentioning in the ASC. He does, however, mention that 'unknowable thousands' of Vikings were killed in these skirmishes, which suggest that the West Saxon burghal system was working, and delivering English victories.