Can you use split second spells as a way to stop counterspells?

Split second (CR 702.61) means that while the split second spell is on the stack, no player may cast other spells or activate non-mana abilities. Since counterspells are spells themselves, an opponent cannot cast a counterspell in response to your split second spell. This makes split second an effective way to push something through that would otherwise be countered.

However, split second does not stop everything. Players may still activate mana abilities, and — critically — triggered abilities will still trigger and go on the stack even while a split second spell is waiting to resolve (CR 702.61b). So if your opponent controls a permanent with a triggered counterspell effect (like Mystic Snake's trigger), that trigger can still occur.

Also note that split second only lasts while that spell is on the stack. If somehow the split second spell is removed from the stack (e.g., exiled by a triggered ability before it resolves), the restriction ends immediately.

Concrete example: You cast Krosan Grip (which has split second) targeting an opponent's artifact. Your opponent wants to counter it with Counterspell, but they cannot — Counterspell is a spell, and split second forbids casting spells in response. The Grip resolves and destroys the artifact.

Bottom line: split second is a powerful tool against interaction-heavy opponents, but it is not completely immune to all responses — triggered abilities and mana abilities are notable exceptions under CR 702.61b.