grab at (someone or something)
To attempt to seize or grasp someone or something. The man grabbed at me as I walked by, so I sprayed him in the face with pepper spray. I tried grabbing at the paper in her hand, but she snatched it away from me effortlessly.
grab at someone or something
and grab for someone or somethingto grasp quickly at someone or something; to try to seize someone or something. He grabbed at me, but I got away unscathed. I grabbed at the rope, but missed. The teacher grabbed for the little boy and held him.