Basic how to play:
Line up vocabulary cards on the board in one long horizontal row. If they don't all fit, just use enough to fill up the board from end-to-end.
Two students battle. They start on opposing sides of the board and read the vocabulary cards in order, moving towards each other. When they reach the same card, they play janken. The loser has to return to the side they started from and start again. The winner gets to keep moving forward. They keep playing until one person reads all the cards from one side to the other.
Notes/tips:
This can take a long time. It's best to set a timer (or at least keep an eye on the clock) and after 2-3 minutes, have them play janken to declare a winner if no one has won yet.
Played this way, only two students play at a time. If you want, you can make small sets of picture cards for pairs of students and have them put their desks together, line up the cards, and play in pairs sitting at their desks (I haven't tried it this way, but I imagine it would work okay!). To involve other students, you can also assign them roles like timekeeper and calling "ready... go!"
I usually ask for volunteers. Final champion gets to play against the ALT.
I usually also strategically order the cards so the difficult ones are clumped in the middle. That way, no one starts out at a disadvantage.
If there's anything unclear, please let me know!