Don’t get the gears in running engine

Hello, actually the title already says everything: Today I drive from the highway, want to switch to the 4th and notice that I can not get it in. First stop and push in with a little force…. But then came a “crat” from below. I immediately took the Gan out again. When the engine is off, the gears go in perfectly. Then I turned off the engine and put in the first gear. At the start the car went forward. Please don’t guess now that I the clutch should step 😉 Now my question: Is the clutch limp or can it be something else? Something with the clutch has to be… Greeting Lexenewax