subtle

sub+tle(title) without subtitle it is difficult to understand the other languages

subtle:substitute,if a main player is down,then coach will substitute him and the the substitute is not known n difficult to detect....

SUB(down)+TELL- so down that it is difficult to tell/percieve

see SUB+ btle sounds like BATTLE a subject which acts like battle is very difficult to decipher or understand

subtle:-The people who are cleaver always destroy subtract tail so that nobody can find them.