"Do the right thing", in this context, goes beyond just the presence or absence of typechecking.

But regarding type checking, Lisp (at least Common Lisp) is strongly typed. Really, very strongly typed (for example it will complain about putting a "byte" in a "character" array; or of using an "array" when a "simple-vector" was expected... Lisp is very nitpicky regarding types!), but the type checks happens mostly at runtime. Some checking also happens at compile time, even more if you intentionally include type declarations. (Type declarations are part of the ANSI Common Lisp standard.)