When tipping a lawnmower the lawnmower should be tipped backwards with the handles facing downwards and not on it's side unless changing the oil.
When changing the oil you can tip it on the oil cap side if needed to drain the oil or if possible use the oil drain plug located underneath the engine.
A riding lawnmower should also lifted upwards in the air and not tilted on it's side to prevent oil from getting into the wrong places.
When you tilt a lawn mower and tilt it so that the carburetor faces downward it can cause fuel and oil to leak into the engine.
When fuel and oil leak in the lawnmowers engine it can lead to engine damage and difficulty starting the engine.
When you tilt a lawnmower it causes oil and fuel to flow into areas where they shouldn't be due to gravity such as the air cleaner, carburetor and even the engines cylinder.
If you have the lawnmower tilted so that the carburetor is facing down, oil can leak out of the breather tube and even lead to major oil leaks.
Oil and fuel that gets into the wrong places of the engine can cause issues such as fouled spark plugs, difficulty starting the engine, engine smoking and engine locking up.
And if the lawnmowers engine is tipped or tilted in a way which allows the fuel to pool in the cylinder, it can then cause a hydro lock to occur which is when the engine cannot start or runs poorly.
When you need to tip a lawnmower you should ideally tilt the lawnmower backwards with the handles on the ground instead of on the side.
Or tip the lawnmower on the oil cap side for oil changes so that oil does not pool in areas that can cause problems.
Also never tip a running lawnmower as it can cause debris to be thrown out at high velocity and cause injury or even death.
And never reach under or allow anyone else to reach under a running lawnmower as that too can be deadly and cut your hand off.