Iroha karuta, or just karuta, is a game that has its roots in Japan from over 400 years ago. Based on a Portuguese game brought over in the late 1500s and early 1600s, when they were trading in Nagasaki, karuta has pairs of cards. Each pair consists of a picture card and a reading card; both cards share the same hiragana character.
There are several ways to play the game, but one common way is to place all the picture cards face up, and deal the reading cards to the players. Each player reads one of their reading cards, while the other players try to pick up the correct picture card. I occasionally play variations on this game while teaching English; it and many other traditional Japanese games are still played today by elementary school students!
Reading cards have the player's name and information printed in Japanese text, surrounded by a border with lots of different sports equipment and a flag. Backs of all cards have a design like you see above.
As the pictures are color pastel drawings, the images are nice. Finding a full set probably isn't easy or cheap, partly because the set includes Wally Yonamine, a popular foreigner, and Masaichi Kaneda, considered one of the best pitchers of all-time in Japan. Of course, other popular players of the era appear in the set.
My card above is of Chusuke Kizuka, definitely a common baseball player from the set. He is a member of the Hawks. That isn't to say that he was a bad player - Kizuka was a six-time All-Star, hitting over .300 a few times in his career; he also was pretty good on the basepaths, ranking in the top 5 all-time. His career batting average was .262 and he managed 479 steals in 593 attempts, which gives him the best percentage of those in the top-five SB category. His success as a base stealer certainly is the reason he is depicted sliding in his card above.
The JK20 set contains stars from all sorts of sports - university and professional baseball players, ice skaters, swimmers, judo and discus stars all appear in the set. This is in contrast to JK19, which only has baseball players.
Note: this post was edited thanks to SumoMenkoMan's comment (see below). I originally had this labeled as JK20, and changed my mind while writing this post - but thanks to him I know I was right in the first place. As SumoMenkoMan mentions, JK19 has a different font and (I couldn't notice this when I looked at the image in the first place) parenthesis around the team name in addition to the position in the lower left corner.