A simple comparison of the twos size and weight immediately demonstrates that answer.
Above: this is an adult male leopard, note how small it’s head is next to hers. She dwarfs him. (Unf he didn’t make it)
A lioness is typically more than twice the size and weight of a leopard. Most lionesses weigh over 300lbs, compared to a leopard who rarely exceeds 150.
When it comes to strength, size is the determining factor. Bigger cats are inherently stronger; just 20lbs on a feline adds considerable power. Male leopards are incredibly powerful cats, but not even close to that of a lioness.
As for speed, that can really vary on the individual. Even in a lion pride, lionesses have huge ranges in speed…which dictates their hunting role. With the fastest lionesses being chasers, & slower being catchers. The fastest being close to twice the speed of the slower females.
If we are comparing the fastest lioness to the leopard, they’re relatively close in speed. I’ve personally seen instances where lionesses were clearly faster when chasing a male leopard and vice versa. So, its literally an individual basis for both, not species. The following photo sequence showcases an instance where a lioness is clearly faster, demonstrated by how quickly she closes the gap between them.
From what I can gather, this question is merely asking for a comparison of a lionesses strength/speed vs a male leopard, not whether one can “defeat” the other…despite it using that term.
I see now, other answers perceived it as who could defeat the other, so I’ll just close with some stats on this from a study:
We ascertained cause of death for 52% of lion mortalities (n=333) and 45% of leopard mortalities (n=433) (Figure 4). Conspecifics were responsible for the greatest percentage (lion: 69%; leopard: 40%) of known-cause mortality for both species. Leopards accounted for 3% of known-cause juvenile lion deaths (n= 121); leopards were not recorded killing lions older than 7 months. Lions accounted for 22% of known-cause leopard cub deaths (n=152) and 23% of independent (≥2 years old) leopard deaths (n=44). The mean age of lions killed by leopards was 0.22 ± 0.12 years (range= 0.08–0.58 years), while the mean age of leopards killed by lions was 2.71±0.75 years (range=0.08–16.59years).
These kind of questions are almost literally comparing apples and oranges, as leopards are technically the strongest big cat lb for lb, but not close to as strong as a lioness. They’re just very different felines.
& when it comes to lionesses fighting male leopards, they CAN hold their ground and survive. Defeat her? No. But, it’s not necessarily a given she defeats him either. It can be circumstantial. But, very few leopards would choose to stand and fight, they will try to run and get up a tree. In the first photo sequence, the lioness prevents him from getting up the tree and damages his hind legs to the point he couldn’t climb back up.