Thanks for the query.
Usually during intercourse the vaginal discharge
will increase and intercourse can cause small abrasions on the vaginal mucosa, that can lead to little bit of spotting.
So may be these two presented in mixed form as brown stain.
As you had intercourse in the non-ovulatory period, there is very less chance for pregnancy
So, don' t worry. Wait for the next period.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429