He put his hand on the back of the chair.

I moved my hands to the back of his chair.

Then his hand was on the back of her chair.

She held on to the back of a chair for support.

I put my hand on the back of a chair.

She reached for the back of the chair with both hands.

I sat very straight against the back of my chair.

If he was shot sitting down there would probably have been blood on the back of his chair.

He reached behind himself and did something to the back of his chair.

People often use a table or the back of a chair for this.