Try this:
CREATE TABLE SEASON( season_id INT NOT NULL, start_date DATE, end_date DATE, PRIMARY KEY(season_id)) ENGINE = INNODB;
CREATE TABLE PLAYER( player_id INT NOT NULL, first_name VARCHAR(15) NOT NULL, last_name VARCHAR(15) NOT NULL, position VARCHAR(15), first_season_id INT, last_season_id INT, height_feet INT, height_inch INT, weight INT, college VARCHAR(30), birthday DATE, PRIMARY KEY(player_id), FOREIGN KEY(first_season_id) REFERENCES SEASON(season_id) ON DELETE CASCADE ON UPDATE CASCADE, FOREIGN KEY(last_season_id) REFERENCES SEASON(season_id) ON DELETE CASCADE ON UPDATE CASCADE, CHECK (height_feet > 0 AND height_inch >= 0 AND weight > 0)) ENGINE=INNODB;
It adds season_id
as a primary key.