NASA's first successful lander was the Viking 1 lander in 1975. Since then, NASA's missions to Mars have increased in number and complexity. While NASA's stated ultimate objective is bringing humans to Mars and back, an intermediate goal is that of sample-return, bringing a sample of material from the surface of Mars back to Earth. Given a 2-year trip each way, a mission tenatively planned to launch in 2026 would return samples to Earth around 2030.
SpaceX has been working on its own "Mars" program, the Starship. Elon Musk has claimed that the Starship may launch for Mars as soon as 2024. Such a mission would land on Mars in 2026.
Will NASA return a sample of material from the surface of Mars to Earth before SpaceX Starship lands on Mars?
The resolution of this question depends on the relative timing of two events:
1) A mission substantially (>30%) or wholly funded by NASA successfully returns a sample from the surface of Mars to Earth.
2) A rocket build by SpaceX designated as "Starship" or clearly designated as a successor to Starship successfully lands on Mars.
The question will resolve positive if event 1) happens before event 2).
The question will resolve negatively if event 2) happens before event 1).
If neither of these events happens before the closing date (2035) the question will resolve ambiguously.
Note that the following series of events would result in a negative resolution: SpaceX builds a Starship rocket which is purchased by NASA. That rocket lands on Mars successfully. That rocket returns to Earth with samples from Mars in it. Because the SpaceX Starship landed on Mars before the NASA mission returned samples to Earth, the question resolves negative.
Similarly, the following sequence of events would resolve positive: NASA contracts a Falcon Heavy from SpaceX for one of its missions. That mission successfully returns samples to Earth before Starship lands on earth.
It is also worth noting that if both NASA and SpaceX hew to their currently claimed timelines, Starship will land on Mars in 2026, 4 years before a sample return mission is completed in 2030.