Fall chasing runners in exploratory part of course (5,4)
I believe the answer is:
field trip
'exploratory part of course' is the definition.
The definition suggests a singular noun which matches the answer.
'fall chasing runners' is the wordplay.
'fall' becomes 'trip' (as in tripping over).
'chasing' means one lot of letters go next to another (some letters chase after others).
'runners' becomes 'field' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'trip' put after 'field' is 'FIELD TRIP'.
'in' is the link.
Can you help me to learn more?
(Other definitions for field trip that I've seen before include "scientific expedition" , "Expedition by students or scientists" , "Expedition to study" .)