Train strike's beginning, which creates worries (9)
I believe the answer is:
exercises
'train strike's beginning which creates worries' is the definition.
The definition and answer can be both related to natural events as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'train strike's beginning' is the wordplay.
'train' becomes 'exercise' (I've seen this before).
'strike's beginning' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'exercise'+'s'='EXERCISES'
Can you help me to learn more?
(Other definitions for exercises that I've seen before include "trains" , "Muscle movements to promote fitness" , "Multiple repetitions to train" , "Keep-fit activities" , "Exertions to develop endurance or skill" .)