How to convert strings numbers to integers in a list?

The data looks like you would know in which positions the numbers are supposed to be. In this case it's probably better to explicitly convert the data at these positions instead of just converting anything that looks like a number:

ls = ['batting average', '306', 'ERA', '1710']
ls[1] = int(ls[1])
ls[3] = int(ls[3])

Try this:

def convert( someList ):
    for item in someList:
        try:
            yield int(item)
        except ValueError:
            yield item

newList= list( convert( oldList ) )