Excellent--A topic I am intimately familiar with.
First off let me state I am a Runner in deference to Mochiman's statement. I was given the status All American in high school for three miles (my whole starting varsity team was actually AA) and can still twelve years and many years of hard contact later can still cut a three miler in 18 minutes cold.
I have also much experience carrying knives running. There are a couple factors you need to take into account when running and thinking about knives. First, your fine motor skill are going to be shot if you need a knife in a hurry. Better have a very well practiced way of getting your knife if you wanna protect yourself with it. I carry in the front of the waistband a spyderco Endura fully serrated when it is warm out. if you are running hard, you may have the same experience with the SOB carry as I did, my butt muscle actually displaced the knife totally with movement many years back. Clatter Clatter never carried since then in SOB, metal clip may change my mind on that some day, but I still prefer the standard plastic clip knife. It fits better and comes out easier, but also stays in place as I need it. It id not come out when I dumped my bike bad a few years back.
Next question, what is your climate? As the Mochiman says, the nylon shorts are prefered. actually, I disdain true running clothes, figuring the nylon shorts with the hip seam split to be too faggy in appearance for my insecure self. Summer I wear the columbia whidbey shorts, the ones with the zipperd rear pocket (amazing how often the post run snickers jones takes a hold of me) and the elastic belt integrated (very handy to keep your clip in place IWB front between your hip and pelvis.
But in Chicago, we also have winter, where it seems everyone with a Rott or Pit just is too f()cking lazy to walk them properly, on a leash. Getting to a pocket knife clipped to your waist, especially if you are cold, hands are wet, its raining/ sleeting/ snowing and windy as hell, is bascially impossible. I bought from Marion David Poff a couple years back a spyderco Moran with an edgeworks kydex "neck sheath" Now I detest neck knives, and they will be useless inside your clothes in winter. I took a neck sized paracord loop and put my wrist thru it instead of my head, then wrap the cord twice, wioth enough slack to comfortably carry it in the weak side hand. It is invisble/ or at least very unobtrusive at almost any time of day, you have a very sharp knife with an excellent grip for retention either forward or reverse grip and the pommel is pointy but non lethal, so the labrador retreiver or small yappie mutt (either variety) who jumps to close can be poked and told gently to get back without actually harming it. Additionally, this carry retains it if i fall without is being strapped rigindly to me when I hit the ground, pretty important if you wanna avoid injury.
Around here, I do not have too many issues with people, but many with dogs, particulalry since getting a small one myself. Dogs coming at you in cold weather can be a real problem, as they do not seem to be as affected by inclement weather as we are. on the other hand, I would be comfortable enough using the Moran or spyderco with two legged trouble as with four. I prefer the Moran becasue there is no lock to worry about, and I do not have to adjust my grip in the cold or under duress, just grab it and go.
I have been running since I was walking and I agree it is good defense, but I have carried a blade wit me while doing it for 16 years. In the summer, go ahead and carry in the waist, but in winter, modify your game for a bit of flexibility.
To address the issue of carrying a folder in your hand, better have it lanyarded to your wrist, or the first time you fall you will drop it into a sewer grate or river (Mr. Murphy likes to make unscheduled appearances at all my social events)
Good Speed to you friends.
BTW, I usually run alone, I cannot do CPR to myself, but great advice for pack runners!!)
Email me if you want a pic of this rig for the moran and a pic of it in carry mode.
Parker