Sentence:  ... first comes the case of tenants with a customary right to <WSD>shack</WSD> their sheep and cattle who have overburdened the fields with a larger number of beasts than their tenement entitles them to, or who have allowed their beasts to feed in the field out of shack time. 
Meaning of the word marked with <WSD> tags:  To feed in stubble, or upon waste.