Or you can look at it from a bivalent logic point of view.
The OR logic gate gives 'true' results if both statements are 'true' or when just one is 'true' (in effect the OR is a combination of XOR and AND).
The AND gate gives 'true' only if both statements are true.
The XOR gate (either A or B) gives 'true' only if one statement is false and the other true.
Applying this to the rulebook wording, Big Hand applies to tackle zones OR pouring rain. It's not either one condition or the other nor both conditions simultaneously (if it was written with 'and' instead of 'or').
<pedantic mode off>