I created this tutorial because I have seen baseballs and various objects combined and I wanted to see how I might go about re-creating these images.
I came up with this as the final image.
I started with a couple of stock art photos and inserted the baseball in a layer over the melon.
Reduce the baseball layer's opacity and align and resize the baseball to fit on top of the melon using the transform tool.
Restore the baseball layer opacity to 100% and change the layer blend mode to "multiply" to get the laces to appear part of the melon.
This gets you pretty far down the road and you could stop here to have a fair chop. I chose to add a layer mask to clean up some of the surface grunge from the baseball image that the red arrows are indicating. A quick layer mask can reduce the baseball to where only the laces show along with some white leather near the laces.
This helped clean the image but the laces looked a little dull to my eye. I added a Hue/Saturation adjustment layer above the laces to help restore the dullness created by the layer blending. If you did not create the adjustment layer as a clipping mask (like I normally do), it will also affect the baseball layer below. Right click the adjustment layer and select "Create Clipping Mask" to limit the affect of the adjustment layer to the layer below.
The adjustment layer helped, but when you look closely at the image, you can see where the red laces blend with the dark green stripes of the melon and give an undesirable transparent feel.
To correct the laces without loosing the effect needed to make the rest of the image work, I duplicated the baseball layer and mask and placed it above all the other layers, changing the blend mode of this layer to "Normal". I filled this layers mask with all black and then painted quickly in the layer mask to hit the tops of the laces with white to restore their solid un-tinted look.
That was all that was needed to complete the effect and make a fairly convincing chop.