I volunteered last weekend at a local run. A guy from my running club volunteered too and he completely ignored me!
someone being rude to you at your running club? sorry to say, it sounds normal.
i was a member of a outdoor fitness club for several years and had some pretty terrible experiences with other members. ive quit now but imo most members to the one i went to were quite snobby and cliquey. in my experience, fitness/running clubs are good places to get over some social anxieties as your meeting and talking to lots of random people but as soon as they stop being fun, quit.
It's normal...people don't usually always notice others...who knows the other person could be equally shy and hesitating to initiate conversation. Personally I like to just hide in the background, do my stuff and leave without having to socialize.