Cannot add foreign key constraint,MySQL无法建立外键

已经确保1、字段的数据类型或者数据长度一样

2、外键是其他表的主键

求助！！

需要建立外键的表play,代码如下

-- 建play表
CREATE TABLE play
(
    playID INT(2) UNSIGNED NOT NULL AUTO_INCREMENT,
    playerID INT(8),
    gameID INT(1),
    PRIMARY KEY (playID),
    -- 外键约束
    FOREIGN KEY (playerID) REFERENCES players(playerID),  
    FOREIGN KEY (gameID) REFERENCES game(gameID)
);

两个外键涉及到的表，①players表如下

-- 建players表
CREATE TABLE players(
playerID INT(8) UNSIGNED ZEROFILL NOT NULL AUTO_INCREMENT,  -- 空值约束
playerName VARCHAR(20) NOT NULL,    -- 控制约束
playerNumber INT(2) NOT NULL, -- 唯一约束
playerSize VARCHAR(5) DEFAULT 'M',
playerPosition VARCHAR(20),
isSarting ENUM('Y','N'),
PRIMARY KEY (playerID)  -- 主键约束
) ENGINE = MYISAM AUTO_INCREMENT = 15071019 DEFAULT CHARSET = utf8;

②game表如下

-- 建game表
CREATE TABLE game(
gameID INT(1),
gameDate DATETIME,
gameLocation VARCHAR(20),
opponent VARCHAR(20),
PRIMARY KEY (gameID)
) ENGINE = MYISAM AUTO_INCREMENT = 5 DEFAULT CHARSET = utf8;