Employee repairing ball charging hose on 2A ball mill grabbed a 12 lb hammer to knock wedges out while doing so felt a pop in low right back. On 4/10/08 received Rcvid physician report of workability stating restrictions from 4/2/08 through 4/9/08. Restrictions ended as of 4/9/08. Employee did not work on 4/8 or 4/9 as these were normal days off work.