Theres a thread for this called ingame crashing problems but...
If ur so kind to give us ur specs for further detail that might help.
Its probaly coz ur comp can't handle the GFX of transformations and Spirit bomb. Sooo if u type cl_fxquality 0 in the console that should do it. it basicly cuts of all special effects `n stuff try lowering ur resolution and taking off 3d particles and other wot not and see wot happens im not very specific so i wil be suprised if i helped u at all