What if a sample is taken on both the rising and falling edge? I guess your 50 MHz sampling clock would produce a 100 MHz sample rate
if sample is taken on both rising and falling edge, then sample rate Sa/s and sample frequency Hz will be still equals.
For example if you use clock source 50 MHz and use rise and fall edges to produce samples, then you will get 100 MSa/s = 100 MHz = 100 M cycles per second sample rate. Nothing confusing
Sample rate means how many samples per second is produced. If you put strobe for each sample, you will get square wave with frequency which is exactly equals to sample count per second. And it doesn't matter what is source oscillator frequency.