The ornamental design for a pipeobstacle for watersports, as shown and described.
FIG. 1 is a side view, the opposite side being a mirror image;
FIG. 2 is a rear side perspective view;
FIG. 3 is a bottom view;
FIG. 4 is a front end view; and,
FIG. 5 is a rear end view.
The broken lines are boundaries that form no part of the claimed design. The pipe is shown broken away to show indeterminate length and for ease of illustration.