> Zoega glosses koma e-m í opna skjöldu as 'to take one in the rear'

rather than 'from the side' See opinn Z1

In the 'skjöldr' entry he glosses the idiom "to attack in the flank
(from the left)".

Þá kom Yngvarr þeim í opna skjöldu (Yngvars saga víðförla 7).
"Then Yngvar attacked their flank" (trans. Hermann Pálsson & Paul
Edwards).

Þórólfur sótti fram hart og lét bera merki sitt fram með skóginum og
ætlaði þar svo fram að ganga, að hann kæmi í opna skjöldu
konungsfylkingunni (Egils saga 54).
"Th. pressed forward and had his banner carried along he edge of the
wood so that he could position himself for an attack on the king's
flank" (trans. Hermann Pálsson & Paul Edwards).

LN