I dont know if you have ever experienced a pin from guard, but essentially, the guy on the top puts his head on your chest and just holds you down. Which is very easy for him and not so easy for you to attack with submission:
Since there are no chokes in sport sambo, you can only work armbars from that position. Him pinning you, means he will have both elbows closed tight.
That been said, if the top player feels in danger, he can stand up on both feet or lift you off the ground, which will make the ref restart the match from standing:
- One can only submit a grounded opponent
- If shoulders are lifted off the ground, match is restarted from standing
Most wins in sambo happen with combination of throws and pins, which bring most points (you need 8 points lead to technical victory). So a big throw, followed by a 20 sec pin is already the end of the match (4 points for landing on your back + 4 points pin = technical victory).
A player will aggressively attack with submissions if he is behind on points and there is not much time left on the clock, or if the opponent is too good on his feet.