Employee was using a 6"" grinder to cut off the damaged bottom of a barge access ladder. As soon as EE cut through one leg of the ladder, pressure was released and the leg sprung toward EE striking EE's grinder which then pushed and struck EE's left hand against an adjacent guardrail. Diagnosis of 8/18/20: ""Contusion of left hand"". Restrictions given 08/26/20.