A wrestler may voluntarily submit by verbally informing the referee (usually used in moves such as the Mexican Surfboard, where all four limbs are incapacitated, making tapping impossible). Also, since Ken Shamrock (a legitimate UFC competitor in its early days) popularized it in 1997, a wrestler can indicate a voluntary submission by "tapping out", that is, tapping a free hand against the mat or against an opponent. Occasionally, a wrestler will reach for a rope (see rope breaks below), only to put their hand back on the mat so they can crawl towards the rope some more; this is not a submission, and the referee decides what their intent is.