(1) COMPOSITION (CONTENT) Well composed. The diagonal lines of hammer really draw the eye into the frame. This along with the strong use of rule of thirds makes a very powerful composition. The motion blur of the hammer adds a very strong point of interest and really makes the photo work.
(2) BACKGROUND The shallow DOF adds to the interest of the photo by isolating the important elements... the hand and the screw.
(3) CAMERA WORK ,TECHNICAL Exposure is good. Composition is very strong.
(4) DIGITAL PROCESSING ,TECHNICAL There is only one change that I might suggest. The white balance on your camera was not set for the proper color. Although this gives you a very interesting shot, I would be interested to see what it would look like with the proper white balance.
(5)MEETING THE CHALLENGE I might get nit picky and tell you that the item in question is not a tack, but you heard that from most of your commentors.
(6) MY OPINION ON THE PHOTO Interesting shot that gets better the longer one looks at it. Thank you for sharing your vision.
Love the shot and color tones, but I bet you'll get ripped by people cause your subject is not a tack....its a screw or a nail. I dont know if you did this on purpose or if you just didnt have a tack available. Love the motion of the hammer and emotion of the shot. Nice work.