Spike single crochet
A US single crochet reaches into a lower row while its long loop rises to the current row height.
Counted practice swatch
Make four rows of 15 sc. Use an alternating pattern of one normal sc and one spike into the stitch two rows below.
Work the repeat
Insert in the lower stitch, draw up a loop to the height of the working row, yarn over and pull through both loops. Skip the current-row stitch directly above the insertion so the count stays 15.
Read the fabric
A spike replaces its corresponding top stitch. A loop that is too short pulls the rows together; a loose loop makes a snag.