Field protector (4)
I believe the answer is:
tarp
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">field protector</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tarp that I've seen before include "canvas sheet" , "Cover" , "Bail-out" .)