basically you just have to play a match at every stadium heres a list for you:
anfield
Amsterdam arena
Bristol mary stadium
Camp nou
El Monumental
Estadio do pragao
estadio jose alvalde
estadio da luiz
estadio amazonas
estadio de palenque
guiseppe meazza
konami stadium
mohamed lewis stadium
old trafford
san siro
santiago bernabeu
saitama stadium 2002
stade de france
stade louis II
stadio olympico
ville marie stadium
wembley stadium
there are 22 overall and you have to finish every match but not win online mode does not count become a legend does count