The scholars mentioned two meanings about this verse:
The first: The subject of the verb (fear) is Allah (swt), which means that He (swt) is not questioned about His judgement, no rebound for His decision and He (swt) does not fear anyone of His creation when He brings down punishment upon His deniers. This is a strong threat towards the people of Makkah.
The second meaning of this verse: The subject of the verb (fear) is the person who hamstrung the she-camel of Allah (swt) and doesn’t fear any consequences for his evil action. He did it with the agreement of his people and with stubbornness, determination and denying the prophet Saleh (pbuh), consequently, they all deserved the punishment.