The ornamental design for a tennisracket, as shown and described.
FIG. 1 is a first perspective view of a tennis racket;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The portions having different stippling illustrate a contrast in the appearance of the tennis racket, with no particular color, texture or finish being claimed. The portions of the tennis racket depicted in broken lines in the drawings, including the gut strings form no part of the claimed design.