After September losses, and with U.S. stock market on track for a third weekly drop, talk of a correction is back in vogue, but market strategists say the will have to first breach its 200-day moving average, which has held amid all the recent down days.

"If you break below 1,900, or the 200-day moving average, a psychological floor, then we'd see selling accelerate," said Sean McCarthy, regional chief investment officer for Wells Fargo Private Bank.