1 letter:
.

3 letters:
ace, act, add, bag, big, bow, boy, end, jar, pen, pun, rag, ref, run, set

4 letters:
balk, blow, book, bout, cast, chip, club, cool, curl, dice, down, drum, dull, flop, game, goal, golf, half, harp, hero, hoot, jazz, jolt, lark, legs, life, make, nine, open, part, pass, pipe, plot, prop, riff, role, romp, ruff, sign, slur, smut, snap, soil, todd, turn

5 letters:
about, amiss, amuse, break, bugle, carry, chord, clean, cover, dormy, enact, enter, error, field, frame, frisk, guard, heavy, house, jacks, lento, lousy, paint, rerun, round, scene, score, scrum, serve, shark, shtik, skirl, sneer, sport, stage, stand, start, study, swing, third, trill, trump, words

6 letters:
adagio, appear, assist, author, cavort, center, chorus, climax, dabble, dormie, epilog, fantan, female, fiddle, figure, frolic, fumble, gamble, gambol, grotty, ground, inning, inside, legato, monkey, notice, onside, otiose, paddle, period, putout, quaver, razzle, replay, retire, review, romper, ruffle, script, sequel, sevens, speech, tackle, tamper, twofer, vivace, wanton, warble

7 letters:
act out, allegro, amateur, bassist, bezique, blocker, booking, burbage, casting, co-star, connect, costume, cricket, croquet, disport, dry run, fireman, handoff, hugging, ingenue, kissing, megahit, misplay, musical, mystery, necking, opaline, outside, passing, persona, petting, pinocle, pipe up, playday, playlet, playpen, prelude, present, pretend, preview, punning, put out, quarter, reenact, referee, reverse, rollick, rompers, running, sandbox, sandlot, scuffer, serious, service, setting, shocker, shylock, skittle, skylark, support, tartufe, tourney, trumpet, tweedle, unblock, written, wrongly

8 letters:
argument, bang out, bunk off, costumer, critique, cuddling, electric, epilogue, face-off, fondling, fragment, fullback, hardball, libretto, medalist, memorize, modestly, nacreous, opalesce, original, overwork, penuchle, pinochle, playmate, playroom, playtime, play out, position, premiere, pretence, pretense, producer, prologue, property, razmataz, robinson, sandpile, scenario, scripted, serenade, sporting, staccato, suspense, tartuffe, thriller, throw-in, time-out, whodunit, wordplay

9 letters:
backboard, ball club, bandstand, caressing, centering, character, chess set, costumier, entr'acte, favorably, game room, golf club, graceless, harmonise, harmonize, horseplay, jump ball, last half, medallist, memorably, mind game, mousetrap, name part, overtrump, peter pan, playhouse, plot line, rehearsal, represent, rock band, scrimmage, scrummage, seriously, show bill, show card, smash hit, smooching, snuggling, storyline, technical, telescope, touchback, trap play, unactable, underplay

10 letters:
adaptation, afterpiece, allegretto, assumption, beach ball, chessboard, chess club, end-to-end, exposition, extraneous, first half, free agent, indication, iridescent, jackstones, jungle gym, lark about, lymphokine, man-to-man, one-on-one, opalescent, parliament, playfellow, playground, playscript, play hooky, possessive, puff adder, razzmatazz, rock group, run around, sand viper, sight-read, soft-pedal, supervised, symphonise, symphonize, theatrical, theme song, tiebreaker, title role, tournament

11 letters:
accelerando, bewildering, blockbuster, card player, culmination, double play, free agency, full-length, histrionics, nonspeaking, paronomasia, pearlescent, performance, ponderously, quarterback, romper suit, rumpus room, second half, shoot craps, superficies, sympathetic, temperament, tennis club, triple play, uncompleted, unfavorably, utility man, wendy house, whist drive

12 letters:
actor's line, ball carrier, child's play, continuation, curtain call, dramatically, final period, first period, greek chorus, make-believe, make believe, medal winner, miracle play, monotonously, mystery play, on all fours, passing game, passing play, passion play, play reading, play therapy, quarterfinal, running game, running play, sound effect, squeeze play, sudden death, sweeney todd, third period, untheatrical

13 letters:
allegorically, baseball club, baseball play, double tongue, dramatic work, dramatization, extra innings, field general, football play, grand guignol, hognose snake, mise en scene, modernization, morality play, mystery story, outdoor stage, piano teacher, razzle-dazzle, roulette ball, second fiddle, second period, signal caller, skiffle group, splash around, sportsmanlike, stage setting, tennis racket, triple-tongue

14 letters:
curtain raiser, double reverse, dramatic irony, musical comedy, period of play, playing period, representation, review article, scrimmage line, technical foul, tennis racquet, trick or treat

15 letters:
basketball play, critical review, jackie robinson, musical theater, overtime period, pingpong paddle, richard burbage, sleeping beauty, stage direction, theatrical role

16 letters:
costume designer, fielder's choice, table-tennis bat

17 letters:
dramatis personae, exhibition season, line of scrimmage, literary argument, theatrical poster

18 letters:
cast of characters

19 letters:
delusional disorder, fictional character

20 letters:
basketball backboard, dramatic composition, fictitious character, table-tennis racquet

22 letters:
theatrical performance

23 letters:
jack roosevelt robinson