On 04/02/2014 the EE was shoveling sand in sand tunnel & felt a sharp pain in his back/buttocks area. He reported the incident on 04/03/14 to his Supervisor & was taken for MD assessment. EE was not assigned any restrictions, and returned to full duty that day. On 04/29/2014 EE asked reported pain, taken to MD & was given a steroid shot. No restrictions, & returned to full duty.