You may get a broken nose.
That's what happened to this wanna-be assailant when he tackled a woman on a jogging trail. She fought back, and he fled. Read all about it here: http://www.10news.com/news/22074629/detail.html
A common question in my classes is what to do if you're attacked in a relatively isolated area. Many people believe that these potential assailants are a special breed of super-being who have the strength and tenacity of Wolverine with the diabolical malevolence of Freddie Kruger.
Fortunately, most assailants occupy mere mortal human bodies. They have vulnerable points. They are often focused on their attacks and (particularly if their target is female) not expecting you to fight back. In most cases, fighting back will succeed in driving him off. As they did here.