That's his "Play Bark" (WTF?!!?)

Kristin and I went for a trail run today on Wildwood trail. This trail is a great trail in Forest Park (The largest park in any city in the US). We were happily running through the mud and the slop because it was raining out, and has been for a few days. We had made it out to our turn around point and we had not seen a soul because the rain kept everyone away.
On our way back we came around a corner and met two dogs, who barked. We both stopped in our tracks as they were barking, then another dog comes up from behind them, what looked to be a Pit Bull and Boxer mix. This dog went past the other two who had stopped and were just barking cause we scared them too, and this dog came at us growling and barking. I went for the nearest thing I could, which was a hand full of mud. The dog comes up to both of us growling/barking and looking to be the the Alpha. Kristin and I both yelled at him, waved our arms, etc.
About this time I hear from around the next corner as this lady with a baby on her chest who starts yelling at her dogs to come, sit, etc. then she asks us "Do you have a dog with you!" All I could think is WTF, does it matter, you are yelling at your dogs they aren't responding!!! You can see you have this dog growl/barking at us. Next to this lady is three more moderately sized dogs, which makes six, none of them have a leash or collar. Now we have six dogs, one acting agressive, what the hell do you do? The lady can't make her dogs do a damn thing.
Anyways, after this dog makes us aware that he isn't to be trifled with, he calms down, and when the lady stopped yelling he calmed a bit more. At this time I realized we weren't getting hurt, but Kristin hadn't quite calmed down. I started walking further down the path and told Kristin the dogs were fine and lets get going. The lady once she caught up said, that's his "play bark", we haven't been home for 2.5 weeks, so they are full of energy. Play BARK!!!??? What the Heck!!! Seriously a growl followed by a bark is a play bark! Had I had pepper spray on me I would have sprayed the dog. He was growling, barking and running at us and he stopped just short of arms reach when I would have thrown the mud in his eyes and then hit him!
Seriously, don't walk six medium to large dogs without leashes and colars who don't listen to you on a hiking trail. I don't mind dogs, and I don't mind well behaved dogs off leash, but dogs that don't listen and bark/growl, need to be on a leash!

Other than that one moment, we had a great muddy trail run in Forest Park. We both got our butts kicked and running in mud definately makes you work harder.