Appears to be a hydroid but hard to confirm at its' angle in pic
You can rake the frag out and place in a container of tank water and scrape off or brush off with a firm toothbrush and return to tank
I agree about hydroids but it is hard to tell from the pic. Can you zoom in closer? I agree with pulling it out to remove. Other culprits... aiptasia or majano but the form factor doesn't look like these. If you look all of these up you should be able to identify it if you can't get a closer pic to post.