A ball hits a vertical wall horizontally at 10 m/s bounces back at 10 m/s

There is no acceleration because $10\frac{\mathrm{m}}{\mathrm{s}}-10\frac{\mathrm{m}}{\mathrm{s}}=0$

Even though there is no change in momentum there is a change in direction. Hence it has an acceleration

There is an acceleration because there is a momentum change

There may be an acceleration because its initial direction is horizontal