Looks sideways at a bad score by Leslie (5)
I believe the answer is:
ogles
'looks sideways' is the definition.
'ogles' can be an answer for 'looks' (ogling is a kind of looking). I'm not certain of the 'sideways' bit.
'at a bad score by leslie' is the wordplay.
'at' says to put letters next to each other.
'a bad score by' becomes 'og' (I can't justify this - if you can you should give a lot more credence to this answer).
'leslie' becomes 'les' (short for Leslie).
'og' put next to 'les' is 'OGLES'.
Can you help me to learn more?
(Other definitions for ogles that I've seen before include "Leers" , "Looks at (someone) lecherously" , "Looks at amorously, makes eyes at" , "Looks longingly at" , "Casts amorous glances" .)