He's an outdoor cat, so I'm not sure why he does this. He's one year's old and neuteured.

play with it it wants attention...

I have 4 cats :)

He is on a secret mission of stealth to rid the feline world of ankles.

Just kidding, but cats do love to ambush ankles as walk go past. He is just playing.

My cat jumps up and grabs my calf. I like to play back with mine. I raise my hands about shoulder height and make silly noises at him. He runs off a little ways and sometimes comes back for more.

There are four possibilities: 1. the cat want more attention; 2. it's instincts to hunt make it to want to attack the moving things; 3. it's changing it's teeth; 4. it wants to play. I hope I did help you ... Bye !!!

He's playing. Most play mimics hunting and other survival skills. In this case he is stalking and pouncing on your legs trying to get you to pounce back, or for you to fall over and let him disembowel you.

Walk around with a water spray and spray the cat when he does this. Play with him at other times.

Hes just playing and wants more attention. He might also think of them as a toy. lol