Falling behind (7)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">falling behind</span>' is the definition.<br/ ><span class="explanation-format__explanation">('lag' can be a synonym of 'fall behind')</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for lagging that I've seen before include "job in the attic?" , "Not up to date" , "Getting behind" , "thermal insulation?" , "Wrapping used to prevent loss of heat" .)