Show sluggishness, i.e. train sloppily (7)
I believe the answer is:
inertia
'show sluggishness' is the definition.
'inertia' can be an answer for 'sluggishness' (I've seen this in another clue). I am not sure about the 'show' bit.
'i e train sloppily' is the wordplay.
'sloppily' indicates an anagram (I've seen this in other clues).
'e'+'train'='etrain'
'etrain' with letters rearranged gives 'nertia'.
'i'+'nertia'='INERTIA'
Can you help me to learn more?
(Other definitions for inertia that I've seen before include "Stagnating state" , "Tendency not to act" , "Motionlessness" , "I earn it (anag.)" , "Slowness to take action, state of laziness" .)