Gridiron units (5)
I believe the answer is:
yards
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">gridiron units</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for yards that I've seen before include "Three feet in each" , "Pieces of uncultivated ground adjoining buildings" , "Courts" , "belonging to investigators" , "Measures; enclosures" .)