Running after biking

It's pretty normal for quads to suffer and have the "anchor" feeling.  This is especially true for your first few forays into "bricks."

I have a road bike and have, over time, become to enjoy my runs after long rides.  It takes time to get used to, though.  I make a practice of keeping my cadence high, especially toward the end of my rides.  This seems to make it easier to transition.  I feel that if I "mash" the gears at a lower rpm, the muscles fatigue faster (even though HR may be low).  I aid to keep my bike cadence ~ 95 and slightly higher for the last 10 minutes of my rides.  Of course the hills generally knock my rpm's to the 80-90 range.

If your pain is mostly muscular, keep at it and try higher cadence.  If you were experiencing joint pain (knees, hips, lower back, neck), I'd be concerned about bit fit.

When you say half the distance, I'm assuming this is ~1.5 mile run (=1/2 of typical 3mi sprint run).  Try just 5-6 minutes next time and build that each week getting up to 15 minutes of running off the bike.  I recently completed a half-iron with my longest brick of 60 mile ride and 4.3-mile run; exceeding my expectations and making a big improvement vs. the same race in 2007 (2mph faster bike and 15-minute faster run).  I'd say you don't need to go any longer than 15 minutes for your sprint tri brick runs.  Others may disagree, but certainly no need to "over-distance" the brick run.

Good luck and welcome to this wonderful world of triathlons!

Isn't it fun?

I've taken to doing a brick every week just to make it "norrmal" during races.  The first month SUCKED!