While I personally wouldn't try it on someone who was massively larger than me, it definitely has the capability to disrupt the predator mindset of your erstwhile attacker, and put them on the defensive while you follow up with either another strike, or just take advantage of your opportunity to beat a hasty retreat.
Personally, I'm a big believer in the Ball Slap.
Here's another video in the current series at the new Clint Emerson Channel. Don't let the title fool you though, the Spear that is discussed is not the Spearing Elbow technique used by Lee Morrison at Urban Combatives. This the SPEAR as taught by Tony Blauer. In this video though, Pat Mac (Unlike Tony Blauer) is able to get the point and method of the technique across in far less than an hour.
Once again, Clint Smith is joined by Pat McNamara for a brief tutorial. This time Pat Mac covers the Front Kick. Now as Pat Mac himself says in the video, if you're an older guy or just not very flexible, you may want to keep your kick low. Like below the belt level low. I'm personally at the point where I keep any kicks I practice are kept to knee level or below. However if you're still on the right side of 35 or so, the Front Kick to the torso might be for you.
