No wonder I had difficulty making sense of this.

[snip]

> Ok er Guðmundr vissi þetta, þá gerði hann eftir hestinum

> ok ætlaði hjá garði, ok fór eftir honum við inn fjórða
> mann.

[snip]

This appears to be a copying error in our source: ten words
have been omitted. It should read:

> Ok er Guðmundr vissi þetta, þá gerði hann eftir hestinum
> ok ætlaði at hafa í brott. Loftr sá, at Guðmundr tók
> hestinn hjá garði ok fór eftir honum við fjórða mann.

And when Guðmund found this out, he sent for the horse and
intended to take [it] away. Lopt saw that Guðmund took the
horse by [the] home field and travelled after him with three
men.

[snip]