Do I need a team uniform?
No! More than half of spectators at Japanese stadiums wear regular clothes. You'll fit in perfectly in casual wear. That said, wearing the home team's colors (even just a t-shirt in the right color) shows spirit and helps you feel part of the crowd.
Seasonal guide
Summer (June-September)
Light, breathable clothing. A hat and sunscreen are essential for outdoor stadiums. Bring a thin jacket for domed stadiums — the air conditioning can be cold.
Winter (November-March)
Layer heavily for outdoor soccer matches. Heat pads (kairo), a blanket, and a warm drink are essential. Indoor basketball arenas are comfortable year-round.
Footwear
Comfortable sneakers are the only right answer. Stadiums involve lots of stairs, walking, and standing. Leave the heels and sandals at the hotel.