No Matching Signature Error Google BigQuery

I have a table in BigQuery with the following set up:

I am trying to extract the max sport in Column B such that I return:
max_B

Column B is set up as a String according to the schema.

I first tried to make sure the data in Column B could be split up so I can select the appropiate row with the max value to the associated project. I tried the follow query:

SELECT 
SPLIT(Column_B, ",") as split_column_b

This did not work and I then received the following error: "No matching signature for function SPLIT for argument type ARRAY <STRING>".

I then tried to do

SELECT 
SPLIT(ARRAY_TO_STRING(Column_B,":"),",")

However, all that happens is that the table nests as if it were to turn Column_B into a list such as:

| Column_A           | Column_B              |
| ------------------ | --------------------- |
| project783/north   | {"baseball": 0.34243  |
|                    | "hockey":0.09348      |
|                    | "basketball":0.0294   |
|                    | "golf":0.45657}       |
|--------------------+-----------------------|
| project783/south   | {"golf": 0.0615       |
|                    | "basketball":0.5165   |
|                    | "hockey":0.2156}      |

I am not sure how to proceed. When I check the JSON query results Column_B seems to be set as an array and when I try other approaches such as JSON_EXTRACT I receive the "No matching signature" error.

Assuming Column_B has a json string value, you can try below.

WITH sample_table AS (
  SELECT 'project783/north' Column_A, '{"baseball": 0.34243,"hockey":0.09348, "basketball":0.0294,"golf":0.45657}' Column_B UNION ALL
  SELECT 'project783/south' Column_A, '{"golf": 0.0615,"basketball":0.5165, "baseball":0.15684,"hockey":0.2156}' Column_B
),
splits AS (
  SELECT SPLIT(Column_A, '/')[SAFE_OFFSET(1)] AS Column_A,
         TRIM(kv[SAFE_OFFSET(0)], '" ') AS name,
         CAST(TRIM(kv[SAFE_OFFSET(1)]) AS FLOAT64) AS value
    FROM sample_table,
  UNNEST(SPLIT(TRIM(Column_B, '{}'), ",")) e,
  UNNEST([STRUCT(SPLIT(e, ':') AS kv)])
)
SELECT Column_A, ANY_VALUE(name HAVING MAX value) Column_B 
  FROM splits 
 GROUP BY 1;

Query results