I was going through the Detection Spells and looking at the Active descriptor. Then I looked at Combat Senses. Am I right in reading this to mean that after a magician casts this spell his opponents get a willpower (+ Counter Spelling) roll to lower the number of hits? This means, potentially, a magician casting this spell at force 6 could have 6 bonus dice for dodge and surprise but the number of bonus dice will decrease depending on the number of hits his opponents get on their resistance test. I've always just used it as bonus dice at the number of hits the magician got. No resistance test. So which way should I be doing this? Is SR3 clouding my mind again?

Well, good catch there. You are exactly correct about an opposed test for Active Detections. All I can say in defense of ignoring that is the spell descriptor just calls for a spellcasting test and hits, not net hits, add dice to the appropriate pools.

If nothing else, that saves a LOT of die rolling for buying hits calculations...

Good idea there. Easier just to have the grunts at least, buy their hits vs this spell.

Actually, I meant to type "rolling OR buying hits", but yeah, most grunts are only going to be able to buy 0 or 1 hit, so that route isn't too labor-intensive except for remembering which grunts have 4dp minimum in Willpower.

Still, this is really curious because of all the Active detection spells, only Combat Sense affects the subject. All the others "gather information" AGAINST targets and therefore resistance makes sense.