Obtain value of one cell based on value of another cell when both can change

You would either need to use Iterative calculations (ie permit circular references) or use VBA - most would opt for the latter.

If you opt for VBA the obvious question would be: by what means are the values in the matrix updated ?

The other question pertinent to whichever route you go down - will the number of numeric values in the matrix ever decrease ?
If so, what happens when the number drops from 5 to 4 - should the existing value for 5 be removed ?

Using your sample file and the iteration approach (avoiding VBA for time being)

First clear the matrix of scores
I am assuming the matrix represents runs conceded per over (not cumulative) and you're looking to get cumulative snapshots in your table on the left

Second, enable Iteration via Calculation Options (thereby permitting circular references)

Third, add the formulae to B3:B10 such that:

B3: =IF(B3,B3,$D$3*($D$5=$A3))
copied down to B10

Now as you add values to the OBO matrix you should find that at 5 overs, 10 overs etc the cumulative scores will update (and persist thereafter).

Assuming my assumptions are correct the other (far simpler) alternative is of course to make the OBO matrix n by 5 such that each row represents a 5 over segment.
At which point your 5/10/15 table becomes a basic SUM of the appropriate rows.

To elaborate - assume the OBO matrix is now F3:J14 [ie F3:J3 overs 1 to 5, F4:J4 overs 6 to 10 etc...] then

B3: =SUM($F$3:$J3)*(COUNT($F$3:$J3)>=$A3)
copied down to B10

Who said anything about turning off Auto Calculation ?

Attached is your sample file with both suggestions in place - the first is using Iteration, the 2nd is using five over blocks.

When you open this do so in a new instance of Excel