A competitive double may be used in the following situation:
a. Partner has previously bid
b. You bid at your last turn.
c. Neither of you has bid notrump nor established a trump fit, AND'
d. Opponents have found a fit (through 2S).
The double shows values to compete (partnership agrees on the points), and shows weak support/ tolerance for partner (e.g., 2 or 3 cards), and length in your own suit - partner is asked to bid again to help find the best contract.
N E S W
1C 1H 1S 2H
S: Ax H: Jxx D: xxx C: AKQxx